Voters in Germany’s largest state, North Rhine-Westphalia, go to the polls on Sunday, May 13, to elect a new Landtag, the state parliament of NRW.

Politics in NRW, home to nearly 18 million Germans, is often seen as a barometer of German federal politics — it falls in the one-time industrial heartland of Germany, and the state lack neither the leftward tilt of the former East Germany nor the rightward tilt of Bavaria in Germany’s south.  State elections in NRW in 1995 foreshadowed the federal election of Gerhard Schröder, just as NRW elections in 2005 foreshadowed the success of current German chancellor Angela Merkel.

Barring any major surprises, however, the current government headed by a “Red-Green” coalition of the Sozialdemokratische Partei Deutschlands (the Social Democratic Party) and Die Grünen (the Green Party) under NRW premier Hannelore Kraft will improve on its success from the 2010 NRW legislative election.

The SPD has consistently led polls with around 37% to 40% of the vote to just 30% to 33% for the Christlich Demokratische Union (Christian Democratic Union) of Merkel and Norbert Röttgen, who is running against Kraft in the NRW election and who also serves as the federal deputy of the CDU and the environmental minister in Merkel’s government in Berlin.  Early elections were called in March, after the Freie Demokratische Partei (Free Democrats) caused the government’s budget to fail — rather than abstaining from the vote, it opposed the budget, thereby resulting in snap elections.

Given that the CDU has never been expected to win the state election on Sunday, it is unlikely to spur any crisis for Merkel at the federal level, but that doesn’t mean the election won’t have an impact on federal elections — with a German general election on the horizon in 2013, here are four key questions about the NRW election, each of which could ripple through federal politics:

Will the SPD win enough seats to form an outright majority? If the SPD wins enough seats to form an outright majority government in NFW, it will raise Kraft’s profile enormously.  It is not yet certain who will lead the SPD in the 2013 federal election, but if Kraft performs exceedingly well Sunday, expect her name to join the list of potential candidates for the job of chancellor, especially as an appealing foil to Merkel:

Her no-nonsense style and political pragmatism – seen in her cobbling together of a minority government tolerated by opposition parties – are traits often attributed to Merkel.

“You can draw parallels,” said Volker Kronenberg, politics professor at Bonn University. “The two share an openness and pragmatic readiness to compromise which helps them in office.”

But Kraft has one asset Merkel lacks – a human touch.

Using her roots in NRW’s industrial Ruhr heartland to her advantage, she has developed her image as “Landesmutter”, or “mother of the state” which, pollsters say, scores with voters.

Other potential SPD candidates include: Peer Steinbrück, who formerly held Kraft’s job from 2002 to 2005 before becoming minister of finance from 2005 to 2007 in Merkel’s ‘grand coalition’ with the SPD, and Frank-Walter Steinmeier, currently leader of the federal opposition and former foreign minister from 2005 to 2009 and former vice chancellor from 2007 to 2009 in Merkel’s ‘grand coalition.’

How will the CDU’s result affect Röttgen?  Röttgen, too, has ambition to succeed Merkel one day, and if the CDU loses on Sunday, it is likely that his focus will turn back to federal politics.  But his NRW campaign has been seen as somewhat of a failure — his federal ambition has undermined his local credibility, but his attempts to federalize the NRW campaign have made him weaker nationally:

And this week, Röttgen has twice tripped over his tongue. Well behind in the polls, Röttgen made a blatant grab for Merkel’s coattails, insisting that the North Rhine-Westphalia vote was nothing less than a referendum on Merkel’s austerity-driven push to save the euro, which is widely supported in Germany. Many in his party were furious and Merkel quickly moved to disassociate herself from Röttgen’s floundering campaign, saying “the election on Sunday is an important state election for North Rhine-Westphalia, nothing more and nothing less.”

Then, on Tuesday evening, the CDU candidate gave away the shop. During a live television interview, Röttgen was asked: “If you, as leader of the state CDU, want the best for your state, then shouldn’t you go into the opposition if you lose the election?” Röttgen waffled, saying “yeah, well, no I wouldn’t have to, I mean, I should really be elected governor.” Bad enough perhaps. But then he added: “Unfortunately, it’s not just the CDU that makes that decision, but also the voters.”

As CDU support nears 30% — or if it is even lower — an expected loss for the CDU will become a career debacle for one of the CDU’s senior figures and a potential embarrassment to Merkel’s current political position, as she struggles to hold the line on European-wide austerity in the face of anti-austerity success in French and Greek elections last weekend.

Will the FDP be swept out of the Landtag? It was the FDP’s last-minute maneuvering over the budget in March that caused Sunday’s snap election.  So it would be particularly ironic if the FDP is shut out of the Landtag after Sunday’s vote.

Under the proportional representation rules that govern NRW elections, the FDP needs to win at least 5% support on Sunday to win any seats — a number that’s looking dicey in polls for the FDP.

The FDP has been in freefall since joining a federal governing coalition with the CDU in Berlin, and its continued collapse at the state level may well foreshadow a similar collapse in a future federal election, which means Merkel will need to win a majority government or look for a new coalition partner.  The FDP was wiped out in Saarland state elections earlier this year and in Berlin state elections in September 2011, and it lost eight of its 14 seats after last weekend’s Schleswig-Holstein state election as well.

If NRW leader Christian Lindner successfully holds off a rout, he may be primed to replace the beleaguered Philip Rösler as the FDP’s federal party chairman.

How well will the Pirate Party do? Polls show that the Pirate Party may not only win seats in the Landtag on Sunday, but may well hit double-digit support, eclipsing the FDP and perhaps exceeding support for the Greens:

Voters in NRW are fond of the Pirates’ intention of making politics more transparent. “Finally there’s a breath of fresh air coming into politics,” said a 45-year-old woman who had stopped at the Pirate Party information stand in the NRW capital, Düsseldorf.

“We haven’t felt anything like this since Willy Brandt,” said a retired woman in reference to Germany’s chancellor from 1969-1974 who was a Social Democrat known as a politician of the people. But this woman still is skeptical of the Pirates’ ability to bring credible policies to the table.

If the Pirates do enter the state parliament of Germany’s largest state, it will be a symbolic watershed for the young party, raising its profile in advance of national elections, but also adding more pressure on the Pirate Party to be more specific on its long-term policy goals.