Democrat Alex Sink narrowly leads Republican David Jolly in Pinellas County's hotly contested congressional race, according to a new poll that also shows district voters deeply split over Obamacare.

In the hard-fought and nationally watched campaign, 42 percent would vote for Sink, 35 percent for Jolly and 4 percent for Libertarian candidate Lucas Overby, according to an exclusive Tampa Bay Times/Bay News 9/WUSF Public Media poll of likely voters in Congressional District 13. The margin of error was 4 percentage points.

The poll also reveals how the Affordable Care Act has become a virtual litmus test for voters.

Of those who support Sink, 81 percent also support Obamacare. Of those who support Jolly, 84 percent also oppose Obamacare.

Supporters of both candidates felt passionately about the issue.

More than two-thirds of Sink and Jolly supporters said their candidate's position on the law was a "very important" or "somewhat important" reason for their support.

Stephen Gibson, 43, who lives in St. Petersburg and is disabled, said it would be hard for him to support a candidate opposed to the Affordable Care Act "because I think that's not for the well-being of the people."

He said he supports Sink because "she is knowledgeable and trustworthy and from a strong background."

Patty Akil, 55, said she finds Jolly well-spoken and up on the issues, and noted: "One thing I like is he doesn't support Obamacare.

She said she can't imagine backing anyone who supports the controversial health care law.

"The government doesn't belong in health care… it's like a takeover," said Akil, a retired property manager.

Timing, circumstance and millions of dollars have turned this contest into one of the nation's most scrutinized political battles.

The district, which includes most of Pinellas County, is considered a toss-up that could go to Democrats or Republicans. The race comes as the parties are gearing up for nationwide congressional elections, with control of the U.S. House potentially at stake. Outside groups have spent millions of dollars for attack ads against Jolly and Sink.

When pollsters first asked respondents who they would vote for, Sink had 40 percent of the vote, compared to 34 for Jolly, 4 percent for Overby and 17 percent undecided. Five percent either refused to answer or listed someone else.

Pollsters then asked the undecided group if there was a candidate they were leaning toward. Those results found 42 percent supporting Sink, 35 percent for Jolly, 4 percent for Overby and 14 percent still undecided.

Overall, 47 percent of district voters oppose Obamacare, 43 percent support it and 10 percent had no opinion.

Independent voters have the potential to play a big role in the race. According to the Pinellas Supervisor of Elections, about 37.1 percent of district voters are Republicans, 34.7 percent are Democrats and 24 percent have "no party affiliation." (The rest belong to smaller political parties.)

The poll found that independents aren't leaning strongly in either direction. Thirty-three percent of independents backed Sink, 27 percent backed Jolly, 9 percent backed Overby and 23 percent were undecided.

The voters' views on Obamacare may explain the positioning of both major party candidates, who presumably have commissioned polls themselves.

Jolly often campaigns by criticizing Sink for supporting the law while she touts her support of it on the campaign trail.

Jolly has said he would vote to repeal Obamacare, because it's harming individuals and businesses, often limiting choices or raising costs. Sink also brings up the law in ads and appearances, accusing Jolly of wanting to force senior citizens to return to the days of the "doughnut hole" — referring to a much-criticized gap in prescription drug coverage prior to Obamacare.

Republican Rick Gilbert, 61, said he thinks Obamacare amounts to "the seedlings of communism."

He is supporting Jolly as "the best of the evils." He considers himself more conservative than the Republican Party and would consider voting for Overby if he thought he had a chance.

Marsha Ferree, 68, said she supports Sink because women make for better government.

"They're more sympathetic and empathetic," she said. "I just think she's going to be more for the people and more for everyone and less for special interests."

A Democrat, Ferree also said she likes "the idea of the government as a participant that can make our lives better" and believes Sink shares that view.

The telephone survey of 603 registered voters in Congressional District 13 — all likely to vote in the March 11 special election — was conducted Feb. 4-9. The poll, which included respondents using land lines and cell phones, was conducted by Braun Research, a national polling firm based in Princeton, N.J. An independent write-in candidate, Michael Levinson, also is running.