Merkel's credibility at stake in German bailout vote
The 620 members of Germany's parliament, the Bundestag, will shoulder a great weight when they enter the chamber in the old Reichstag building in Berlin on Thursday morning.
They must decide whether to block the expansion of the rescue fund for Greece.
Were they to say "no", the whole effort to keep the eurozone intact would bump up sharp against a block.
On 21 July, at a summit in Brussels, the leaders of the countries which use the euro agreed to expand the size and reach of the rescue fund for countries in difficulty - the European Financial Stability Facility (EFSF).
But dramatic summits and grand communiques cannot deliver on their own. Shaking hands and making a promise is not enough, no matter how powerful the people involved.
In the case of Germany, parliament has to make the final decision - the country's Constitutional Court pointed that out very clearly recently.
So the members of the Bundestag have the power to scupper the expansion of the fund, and throw the rescue attempts of Greece into disarray (not to mention the financial markets).
All the arithmetic indicates that Chancellor Angela Merkel will get the overall majority she needs. The main opposition parties, the SPD and the Greens, have indicated that they will support the expansion of the fund.
But, if the majority is untidy, with the chancellor having to rely on the votes of opponents, that might be interpreted as political weakness at the top - and, moreover, at the top of one of the countries that really matters, as the world tries to avoid a return to recession.
There are definitely rebels in her own camp. At one stage, about a dozen seemed to be in what she might view as the awkward squad, though the number will no doubt change with horse-trading and arm-twisting.
The man in charge of the arm-twisting for the conservative Christian Democrats is Peter Altmeier, the CDU chief whip. He exudes charm and bonhomie, which serves him well as he gauges the strength of the vote.
He told the BBC: "As a chief whip, I have to be optimistic, but so far we have managed to win every single struggle in parliament, every single vote and that is going to happen again this Thursday".
If he is right, and if the overall majority is in the bag, does it matter that Mrs Merkel's majority consists of a cluster of disparate elements?
People around the chancellor insist that a vote is a vote and a majority is a majority. If she gets the victory, the measure goes through and that is what matters. It is not, they say, a vote of confidence in her.
Except that the markets may think that if she has to fight tooth-and-nail simply to get a measure already agreed on through, then the prospect of more help is much diminished - and there are much bigger proposals already on the way.
There are disagreements aplenty. Just within the last few weeks, Chancellor Merkel's position has been contradicted by the leader of both minority parties in her coalition.
The leader of the Bavarian conservative CSU, Horst Seehofer, did not agree with her contention that Europe would fail if the euro failed. "I don't see the connection," he said.
And her economics minister, Philipp Roesler, who is also head of the Free Democrats (FDP), said there should be no taboos on ideas to deal with the Greek crisis - by which he meant talking about allowing the Greek state to go bankrupt.
So, an untidy win for Chancellor Merkel would dent her government, and it might dent any market confidence that the perpetual crisis of the euro has an end in sight.