Prime Minister Mark Rutte will be biting his nails today as he anticipates the results of Monday's Dutch Senate election. He hopes the parties in his coalition government will scrape by with a majority. But the outcome is far from certain - just one seat could make the difference.

That the coalition’s constellation is still uncertain at this point is unusual. As a rule, on the day the Senate is chosen, the results are obvious.

This is because the Senate is not elected by direct popular vote, but rather by the 12 provincial assemblies. The assemblies are directly elected during provincial elections which, this year, took place on 2 March. So why can’t we just count the votes to determine how many seats each party will have?

It’s not that simple
Some regional parties may have representation in one of the provinces though not nationally. These parties have no direct link to the national parties, and it is not always clear for whom their regional assembly members will vote.

Even more importantly, no assembly member is bound to vote for any one individual. They are free to vote for whomever they please.

For instance, a Labour Party assemblyman from North Holland need not vote for a Labour Party candidate for Senate. This year, one Labour assemblyman in North Holland plans to exercise that right. He says he is angry with his own party for supporting a ban on the ritual slaughter of animals. His vote will go to Geert Wilders’ Freedom Party instead.

Voting outside party lines
Voting for another major party is quite rare. But regional parties’ votes are always up for grabs, and there has been intense horse-trading among the majors vying for their votes. Prime Minister Mark Rutte went so far as to meet in his office with an assemblyman from the Party for Zeeland. The meeting proved a successful attempt to win the southern province’s support. Also present there was Geert Wilders, whose controversial Freedom Party supports the coalition and for whom the assemblyman said he will cast his vote.

Mr Rutte was roundly criticized for politicizing the office of the prime minister. The meeting demonstrates how badly he wants a Senate majority, even though a majority is not strictly necessary for his cabinet to carry on. The Senate does not have the power to send a government packing – only the House of Representatives can do that.

Politically vulnerable cabinet
Mr Rutte’s cabinet enjoys the thinnest possible majority in the House of Representatives, one seat. That includes the external support of Mr Wilder’s Freedom Party. In fact, the actual cabinet controls a minority of seats in the House of Representatives.

If Mr Rutte’s minority cabinet fails to win the Senate, it could spell early elections. Though this won’t be immediate – the cabinet can still get legislation through both houses of parliament with votes from opposition parties - the cabinet will be politically vulnerable and inherently instable.

Back when the current cabinet was put together, Mr Rutte himself emphasized the importance of gaining a Senate majority. Today he may just barely make it.