BERLIN (AP) – An election Sunday in Germany’s most populous state is serving as a prelude to September’s national vote. It could give conservative Chancellor Angela Merkel new momentum in her quest for a fourth term – or offer her center-left challenger some relief.

The pressure is on the Social Democrats, led by challenger Martin Schulz, in the election for the state legislature in North Rhine-Westphalia. It is Schulz’s home territory, though he isn’t on the ballot, and home to 17.9 million people, nearly a quarter of Germany’s population.

The western state, which includes Cologne, Duesseldorf and the Ruhr industrial region, has been led by the Social Democrats for all but five years since 1966.

However, polls ahead of the vote – the last test at the ballot box before Germany’s national election on Sept. 24 – now show the Social Democrats neck-and-neck with Merkel’s Christian Democrats.

A defeat for center-left governor Hannelore Kraft would be a major blow for the Social Democrats after poor showings in two previous state elections punctured the party’s euphoria over Schulz’s nomination.

Last weekend, they were beaten by Merkel’s party in Schleswig-Holstein in Germany’s far north.

Merkel’s conservatives in the state, led by challenger Armin Laschet, a liberal-minded deputy leader of the Christian Democrats, have little to lose after a dreadful showing in the state vote five years ago.

They have sought to portray Kraft’s state government as slack on security. They point to burglary statistics, incidents such as the New Year’s Eve sexual assaults in Cologne in 2015 and questions over regional officials’ handling of sometime resident Anis Amri, the rejected Tunisian asylum-seeker who drove a truck into a Christmas market in Berlin in December, killing 12 people.

They also have assailed what they say is regional authorities’ poor handling of education and infrastructure projects.

Kraft’s coalition partners, the Greens, are polling poorly and chances of their alliance keeping its majority look poor. The pro-business Free Democrats, eyeing a return to the national parliament in September after they were ejected in 2013, look set for a strong performance.

And the nationalist Alternative for Germany, or AfD, hopes to enter its 13th state legislature – though its popularity appears to have faded as the migrant influx has receded and the party has been rent by infighting.

The likeliest outcome appears to be a “grand coalition” of the biggest parties led by whoever finishes first.

That would mirror Merkel’s national government, in which the Social Democrats are the junior partners.

After a blaze of publicity earlier this year, Schulz – who chose not to join the government when he returned to Germany after being president of the European Parliament – has struggled to maintain a high profile.

National polls show the Social Democrats trailing Merkel’s conservatives by up to 10 points after drawing level earlier this year.