If today is the first test of the 2014 midterm elections, then Republicans start off on the defensive. The death of Rep. Bill Young after 42 years in Congress forced a special election in Florida’s 13th Congressional District to fill out the rest of his term. The battle between former Young aide David Jolly and failed gubernatorial candidate Alex Sink ends today, along with the open seat in the narrowly Republican district:

Republicans have relentlessly focused on Sink’s support for Obamacare, which she says she supports even if it is not perfect and still needs some fixing itself.

“We can’t go back to letting insurance companies do whatever they want,” she says in a television ad, the Associated Press reported. “Instead of repealing the health law, we need to keep what’s right and fix what’s wrong.”

It has become the signature issue of the race, and Republicans hope that a win could preview the November elections by illustrating how toxic the healthcare law has become for Democratic candidates, specifically vulnerable Democratic Senators targeted by the GOP this cycle.

If Sink were to win, on the other hand, it could embolden Democrats, demonstrating that support for the healthcare law was not the albatross that some have made it out to be.

The Hill’s Alexandra Jaffe wonders whether either candidate deserves to win so much as to not lose:

Lackluster candidates, millions spent, a third-party candidate: Every detail of Tuesday’s special election in Florida’s 13th District makes it unusual, but the bellwether district is still the first indication of the 2014 electoral mood.

Regardless of outside factors in the critical region, the winning party will try to spin the results of the first midterm test as a harbinger for their party’s messages this fall.

“This is not about [Democrat] Alex Sink and [Republican] David Jolly,” said Mike Fasano, a former Florida GOP state House and Senate member. “This is about what’s happening in Washington and who happens to be more unpopular than the other party.”

Stakes are highest for Democrats, even though they don’t hold the vacant seat once held by the late Rep. Bill Young (R-Fla.).

Facing a 17-seat deficit in the House, Democrats can’t afford to lose one of the few toss-up seats left in the country. Such a failure would undercut their message that they can put GOP-leaning seats on the map or even compete in places where President Obama narrowly won in 2012.

Of course, one could argue that Republicans need to show that they can hold swing districts in the absence of incumbents, too. This Congress has already seen a number of retirements on both sides of the aisle, after all, and there may still be time for a few more. If the GOP can’t hold its R+1 districts, even in a special election when voting patterns may take surprising twists, it might not look good for Republicans in November.

There hasn’t been much polling in this race, which is typical for special House elections, but what polling exists shows a toss-up. PPP puts Sink slightly ahead at 48/45, with another 6% going to a Libertarian Party candidate, and that’s with a sample with an R+7 edge. Only 21% of that sample was below 45 years of age, too, which may well reflect the electorate in a special election, but won’t help Sink much.

The US Chamber of Commerce poll puts Jolly ahead 44/42, though in a smaller sample. The bigger takeaway from that poll is that ObamaCare — which Sink supports — is underwater in the district, 39/54. Interestingly and tellingly, PPP never bothered to ask that question, which has been the biggest policy issue in the campaign. Instead, PPP asked a question about the prioritization of “climate change” agenda, where only 44% thought it was “very important” — opposed to 25% who thought it was “somewhat important,” and 29% who thought it was “not that important.”

This one is too close to call, but will be fascinating to unpack when it’s over. The winner will have to fight this battle again in the fall, too, for another term. It might be a day or two before we know which candidate has to worry about it.

Update: Guy Benson e-mails me to note that Barack Obama won this district in both of his presidential elections, which shows the nature of this swing district; Young won it both times for the GOP. Obama’s turnout models won’t be what we see today, though.