US election 2016: Cruz and Kasich team up to slow Trump
Donald Trump's two rivals for the Republican party's presidential nomination have announced they will now co-ordinate strategies against him.
Ted Cruz will cut campaigning in the Oregon and New Mexico primaries to help John Kasich, while the latter will give Mr Cruz a "clear path" in Indiana.
Mr Trump said his rivals were "totally desperate" and "mathematically dead".
He has a clear lead in delegates but may still fall short of the 1,237 needed to win outright.
If he does not reach the target, the vote will go to a contested convention - where a different nominee may emerge through negotiations among party figures.
Donald Trump currently has 845 delegates, Mr Cruz 559 and Mr Kasich 148.
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How was the pact revealed?:
Mr Cruz and Mr Kasich announced their move in near-simultaneous statements.
Mr Cruz's campaign manager, Jeff Roe, said: "Having Donald Trump at the top of the ticket in November would be a sure disaster for Republicans. Not only would Trump get blown out by [Hillary] Clinton or [Bernie] Sanders, but having him as our nominee would set the party back a generation."
John Weaver, Mr Kasich's strategist, said in a statement released on the Team Kasich site: "Our goal is to have an open convention in Cleveland, where we are confident a candidate capable of uniting the party and winning in November will emerge as the nominee."
How has Donald Trump reacted?
Mr Trump's first reaction was to tweet, condemning his rivals as "totally desperate".
In a later statement, he said it was "sad that two grown politicians have to collude".
"Collusion is often illegal in many other industries and yet these two Washington insiders have had to revert to collusion in order to stay alive," he said.
Mr Trump said Mr Cruz' s campaign was "in freefall", whereas Mr Kasich had fewer delegates than Marco Rubio, who suspended his campaign a month ago.
He again complained of a "rigged" party electoral process, adding: "This horrible act of desperation, from two campaigns who have totally failed, makes me even more determined, for the good of the Republican Party and our country, to prevail!"
Mr Trump's campaign has featured controversial comments and policies, including calling some Mexicans rapists, vowing to bar Muslims from entering the US and pledging to build a wall on the US-Mexican border.
However, Mr Trump did last week promise to change his image, in a closed-door meeting with Republican party leaders.
Where and when are the forthcoming Republican primaries?
The voting system is complicated, and delegation allocation varies state by state.
The Indiana primary (57 delegates) is on 3 May, Oregon (28) is on 17 May, with New Mexico (24) on 7 June.
But before those comes voting in five north-eastern states where Mr Trump is favoured.
Maryland (38), Rhode Island (19), Connecticut (28), Pennsylvania (71) and Delaware (16) all vote on Tuesday.
Will the pact have any effect?
The Kasich campaign has been pushing this pact for a while but has been rebuffed by the Cruz team.
Some Republican strategists have also been urging a deal, with the whole focus on preventing Mr Trump from reaching 1,237 contested delegates. The question is, is it now too late to stop Mr Trump?
Indiana is critical for Mr Cruz. That is why he has held a number of events there, largely ignoring Tuesday's votes.
A recent Fox survey in Indiana suggested Trump had 41% support; Cruz 33%; Kasich 16%.
Mr Cruz will hope to pick up Mr Kasich's voters from the latter's stronghold in Indianapolis.
Mr Cruz may believe that because Oregon and New Mexico split delegates proportionately and are unlikely to favour any candidate heavily, he may not lose too much by ceding to Mr Kasich.
Mr Kasich's team believes the two states have similar profiles to the north-east, where he is "performing well". But neither state is likely to play a major role in the main battle to stop Mr Trump.
New Mexico is part of the five-state final voting round on 7 June, when clearly California's 172 delegates will be crucial.
How have US media reacted to the pact?
The New York Times notes that the Cruz-Kasich statements made no direct call for voters to switch allegiance in the named states. It said: "At this late stage, it is unclear how effective the effort might be at swaying voters, especially if the campaigns do not give more explicit instructions."
The Politico website said that the new pact "is an acknowledgment that neither man can overtake Trump in the race... it may still be too late".
CNN says the pact makes sense for Mr Kasich, as his "campaign finished March with only $1.2 million in the bank".
Time magazine reports that Mr Cruz now has a clear lead in "unbound delegates" at the Cleveland convention. This could present "an obstacle for frontrunner Donald Trump if he falls just short of the 1,237 bound delegates needed to clinch the nomination".
What's happening on the Democratic side?
Bernie Sanders spoke to a rally of 14,000 supporters in New Haven, Connecticut, on Sunday, again accusing Mrs Clinton of earning money through "speeches behind closed doors on Wall Street".
Mrs Clinton retains a clear lead in delegates and will hope the north-eastern state votes will effectively put an end to Mr Sanders' dogged campaign.
The pair have traded increasingly hostile remarks in recent weeks.
But Democratic National Committee chairwoman Debbie Wasserman Schultz said: "Regardless of the intensity of what's played out here... we are going to be unified."