With four days to go, Germany's federal election is going down to the wire. Latest polls put Dr Merkel's Christian Democrats (CDU) three points short of re-election with its unpopular coalition partner, the Free Democrats (FDP).
The opposition alternative – the Greens, Social Democrats (SPD) and Left Party – are also three points short of a majority. The election will be decided, not by personalities or policies, but by a modified voting system.
So how do Germans vote? Every citizen over 18 has two votes: the first for a direct constituency candidate and the second for a party. This second vote decides the allocation of Bundestag party seats, with MPs drawn by parties from state lists.
The two-vote system – combining constituency and list systems – is a post-war compromise between the Allies but it is the second vote, the Zweitstimme that counts. The CDU has dubbed it the "Merkel vote", the guarantee that its leader stays chancellor. Their FDP coalition partners claim the same.
Running scared
The party is running scared after it was dumped out of the Bavarian state parliament and government on Sunday. In danger of exiting the Bundestag next Sunday, they are chasing the second votes of strategically-minded CDU voters. They argue that this is the only way to ensure the current coalition is returned – and not a grand coalition or left-wing alliance.
But the CDU has warned voters not to back the FDP, fearing a repeat of strategic voting last January in Lower Saxony when both parties were dumped out of office.
"It's impossible to predict how voters will behave," said Dr Gero Neugebauer, political scientist at Berlin's Free University. "Either CDU voters will back the FDP strategically or else say 'I don't want to waste my vote' and decide to stick with the CDU."
Behind their pre-election squabble lies a curiosity of German federal election law: so-called surplus seats or Überhangmandate.
'Surplus' seats
These arise when a party wins more seats through the first, direct candidate vote than its second vote allocation. Rather than penalise a party for winning additional direct seats, these MPs are allowed into the Bundestag as "surplus" seats.
As this system favoured larger parties it was struck out last year by the constitutional court. On Sunday, a new voting system will be tested for the first time, equalising surplus seats for one party with extra seats for the others.
This means old voting strategies are moot. In the past smaller parties’ voters often backed a larger coalition partner’s direct candidate, who had a better chance of being elected with the first vote; in exchange the larger party’s voters backed a smaller coalition partner with second, list votes.
But the new, untested surplus seat rules leaves the CDU with fears with nothing to gain and everything to lose from an election alliance with the FDP. Determined to give nothing away, Angela Merkel has ruled that everyone fights for themselves. That means on Sunday, all bets are off.
