US mid-terms: Can we tell now if Democrats will win?
Will they or won't they? With the mid-term congressional elections three months away, the biggest question is whether Democrats can win enough seats in Congress to wrest control of at least one of the two chambers and give Donald Trump a bloody nose.
That would have immediate and drastic implications for the president's ability to advance his political agenda and Democratic oversight of his administration.
The "mid-term wave" - a sweeping electoral triumph that reshapes the US national political layout field - is a recurring phenomenon in US politics.
But what is it, and when have they happened before?
"There's really no good definition," says Geoffrey Skelley of the University of Virginia Center for Politics.
"It's just broadly viewed as an election where one party does particularly well to the point where they flip control of a chamber of Congress and also win a sizable number of seats that the other party held."
For the purposes of this analysis, a mid-term wave is where one party picks up a combination of more than 20 seats in the US House of Representatives and the Senate.
That's happened eight times in the last 70 years, notably in 1994 (a Republican wave against Bill Clinton) and 2010 (one against Barack Obama).
Today, the Republican Party is near a modern-day high in seats in the House of Representatives, with a 241-to-194 seat majority, so it could be poised for a tumble.
The Senate terrain may be friendlier for Republicans, with Democrats defending 10 seats in states Mr Trump won in 2016, but this year's political atmosphere is such that an electoral storm could be brewing.
Brewing and actually crashing through are two different things, of course.
Is there evidence pointing to Democratic success? Here are the measurements that will give us clues.
1. Presidential popularity
Mid-term elections are said to be a referendum on the incumbent president.
When presidents are unpopular, voters take out their frustration on their party in Congress.
If the chief executive is riding high, the party is rewarded (or, at least, not excessively punished).
A look at the Gallup presidential approval poll over the last 60 years tends to bear this out.
Every time a president faced a net-negative rating in the month before the mid-terms - Ronald Reagan in 1982, Bill Clinton in 1994, George Bush in 2006 and Barack Obama in 2010 and 2014 - it meant lights-out for his party at the ballot box in November.
The exceptions are also enlightening.
Gerald Ford was plus-24 in October 1974, but his numbers - following his controversial pardoning of Richard Nixon the month before - were poised to take a nosedive, declining 15 points over the next three months.
Democrats gained 48 seats in the House and five in the Senate - what would be known as the "Watergate Class" of Congress.
Lyndon Johnson was around the break-even point in 1966, but unease about the Vietnam War and civil rights unrest, combined with his party's inflated congressional numbers after a big victory two years earlier, set Democrats up for a tumble.
The only trend-defying president was Dwight D Eisenhower in 1958. Even with the US economy in the tank, everyone still liked Ike.
His popularity, however, didn't translate into salvation for Republicans, who lost 48 seats in the House and a stomach-churning 13 senators.
Unlike most presidents, who have started their term with a brief "honeymoon" period of high favourability, Mr Trump entered the Oval Office underwater and has been a political submarine ever since.
His approval ratings have stayed in the high 30s for most of his presidency, only occasionally approaching the mid-40s before diving again. The latest Gallup survey has it at 40%.
Republicans have to hope either the polls are off or Mr Trump once again defies what appears to be an iron-clad rule of US politics.
2. The generic ballot
This involves asking people simply which party's House candidate they would support in the election.
There are 435 individual House of Representatives races every mid-term election, meaning at least 870 candidates from the two major parties plus a handful of prominent independents and third-party politicians.
Each race is unique, every constituency has its own particular interests, and each congressional district has a demographic identity as unique as a fingerprint.
It therefore seems implausible that the collective outcome of all those races could be boiled down to a simple poll asking whether a voter would prefer a nameless Democrat or a faceless Republican.
The generic ballot question, however, has proven to be a remarkably accurate predictor of mid-term election prospects for the two major parties.
"The national generic ballot picks up the national political climate," says Alan Abramowitz, a political science professor at Emory University who has crafted an election prediction model based largely on the generic ballot polling numbers.
"I view it as a measure of the political mood of the electorate."
In 1958, 1982 and 2006, the Democratic generic ballot advantage ballooned before the party's wave-election victories.
When the Republican waves of 1994, 2010 and 2014 swept through, the Democratic advantage narrowed to low single digits (or even, at times during the election run-up, disappeared entirely).
This year, Abramowitz says, the tipping point for Democratic control of the House sits around a seven-point generic ballot advantage. A lead bigger than that, and a wave could be on the horizon.
2018 outlook: The Democratic generic ballot lead has shifted over the course of the past year.
In the late spring it narrowed to the point that it appeared Republicans were in excellent shape for November.
Lately, however, the Democratic lead is approaching double-digits once more.
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3. The economy
Donald Trump and his fellow Republicans are pushing positive economic numbers as a reason why they deserve another two years of unified control in Washington.
Historically, however, a growing economy is no guarantee of success for the president's party.
In 1994, when the governing Democrats ceded Congress, the economy was expanding at more than 4%, although unemployment was a bit higher than the current mark, at 5.8%.
In other wave years, 2006 and 2014, the economy wasn't in bad shape either.
A struggling economy, on the other hand, can be a death sentence for the incumbent party's mid-term prospects.
In 1958, Republicans in Congress faced a bloodbath largely due to that year's recession, which included a modern-record -10% first-quarter GDP contraction.
Negative growth in 1974 and 1982 also probably contributed to Republican losses those years.
"You'd rather have a strong economy than a bad economy, but it doesn't mean you're going to escape the wrath of voters," says Abramowitz.
2018 outlook: With the latest quarterly gross domestic product growth at 4.1% and the nation's workforce approaching full employment, the economic numbers - at least for now - are undoubtedly good.
The economy isn't going to hurt Republican chances in November, but can Mr Trump break with historical patterns and turn them into a positive force?
4. Campaign fundraising
Money makes the (political) world go round.
Levels of cash pouring in for candidates, parties and independent groups are an indication of electoral muscle for advertising, organisation and get-out-the-vote efforts.
They're also a reflection of the enthusiasm of each side's donor base.
No-one likes to bet on a losing horse, and if ballot-box prospects look gloomy, big-money players and grass-roots activists may be reluctant to open their pocketbooks to support their party's campaigns.
Incumbency has a host of advantages, and this is particularly true in the ability to fundraise.
Giving cash to politicians who already control the levers of power makes sense, particularly for business interests and individuals who want to influence government policy.
Giving money to challengers? That takes a combination of faith, passion and a sense of changing political fortunes.
There's one component of campaign fundraising that tracks particularly closely with every wave election in the last 25 years, a period during which the role of money in political campaign skyrocketed.
In the Republican wave of 1994, individual donations to House candidates - which are limited under campaign finance law - tilted toward Republicans, presaging that party's control of the chamber for the first time since 1949.
In 2006, the fundraising advantage flipped to the Democrats, as did control of Congress. Four years later, Republicans were back in the money - and back in charge of the House. In 2014, they built their biggest majority there in 83 years and won control of the Senate, as well.
"In mid-term waves, long-time incumbents can get kind of caught flat-footed when they're faced with a well-funded, competitive race," says the University of Virginia's Skelley.
2018 outlook: If House fundraising is a leading wave indicator, tsunami sirens should be going off in Republican headquarters.
Democratic candidates are setting cash-haul records, amassing more than $419 million so far, with Republicans well behind at $227 million.
By a recent count, 56 Democratic challengers are outraising their Republican incumbent opponents.
There is some good news for conservatives, however. Republican candidates are doing better at fundraising from political-action committees, and - unlike the Democrats - the Republican Party itself has tens of millions of dollars to spend on key races across the US.
When it comes to grass-roots enthusiasm and small-money donors, however, all the chequebook energy and excitement is coming from the left.
5. Political retirements
Set aside all the poll numbers, economic figures and expert analyses.
Who has their finger on the pulse of the political climate better than the politicians themselves?
They're the ones whose names are on the ballots, and they're the ones who will be out of a job or, perhaps, serving in a congressional minority if a wave hits.
Facing the prospect of embarrassing electoral defeat or the loss of congressional agenda-setting ability and plum committee seats in a mid-term wave, some politicians may opt to ease into early retirement or get a head-start on colleagues searching for post-public-service gainful employment.
"We know historically that open seats are more difficult to defend," says Skelley. "And because they're more difficult to defend, that gives the party that doesn't control them a better shot."
A look at modern retirement trends shows a mixed picture. There were years, such as 2006 and 2014, with no apparent correlation between retirements and ballot-box results. The retirement figures in 2010 gave little hint of the carnage in store for Mr Obama's party.
In 1994, however, a surge of Democratic retirements may have foreshadowed big Republican gains that autumn.
The only year with a similarly large differential between the two parties was 2008, a presidential election year, in which Democrats expanded on their House margins and won a filibuster-proof majority in the US Senate.
2018 outlook: If 1994's retirements were a harbinger of doom for Democrats, 2018's numbers could spell trouble for Republicans.
Several key committee chairs and Speaker of the House Paul Ryan have already joined what's become a modern record for retirements from a majority party - a telling sign that they think Republicans may not be a majority much longer.
Micah Luxen contributed to this report.