President Barack Obama and his Democrats face the challenge of limiting fallout from Obamacare and drumming up voter enthusiasm in the November congressional elections, problem areas exposed by the loss of a Florida candidate who had led in the polls.

The defeat of Democrat Alex Sink by Republican David Jolly in a special election last Tuesday has raised anxiety levels for Democrats as they struggle to hold on to control of the Senate in November and pick up seats in the Republican-held House of Representatives.

Paramount on the Democrats' list of concerns about November is the need to ensure that voters feel motivated to go to the polls. Obama won handily in presidential elections in 2008 and 2012, but Democrats lost control of the House in the 2010 midterm elections, when his name was not on the ballot.

The Florida race reflected turnout concerns, as Sink had been leading in the polls in the days ahead of the election. But the party did not get enough supporters to polling stations to take advantage.

"If we'd had better turnout, we would have won. It's that simple," said Democratic Representative Jim McGovern of Massachusetts. "We need to think about how to energize our base."

A focus simply on turnout, however, could distract party leaders from recognizing the dangers presented by the president's healthcare law and, with his approval rating mired in the mid-40s, his relative unpopularity.

The Jolly victory has emboldened Republicans to press their case hard against Obama's signature first-term achievement despite mixed opinions about how big a factor the Affordable Care Act played in the race.

Democrats are aware they will need to be careful in how to handle the healthcare law, which had a disastrous rollout last October and, months later, remains controversial in many respects.

Their strategy? Attack Republicans for wanting to repeal the law and avoid getting stuck in a defensive crouch over it. "Never defend, always attack," said Senator Tom Harkin, an Iowa Democrat who is set to retire.

"People running for re-election are trying to figure out how they are going to talk about it," he said. "Republicans have been good at drilling down that message that it is bad."

White House officials and Democrats rejected Republican arguments that the healthcare law was on the ballot in Florida. They say the healthcare website is now functioning well, and that perceptions of the law will change by November as more people sign up and enjoy its benefits.

"It will improve in the public's mind because it is working, and it will continue to work," said Florida Democratic Senator Bill Nelson.

That is not necessarily a universal view among the party's supporters, however.

"My view is that Obamacare is a plus, eventually. Whether it will be between now and November, I don't know," said Senator Angus King, a political independent from Maine who caucuses with the Democrats.

Obama continues to face tough questions about the law. In a WebMD interview published on Friday, he fielded concerns about the cost of insurance under Obamacare, limits on doctors, and lingering struggles with the website.

Obama used the interview to detail a comprehensive defense of the law ahead of a key March 31 deadline for getting people signed up.

"On a daily basis, we're getting tens of thousands of people who are signing up. We're able to monitor whether there are long wait times on the website, whether things are getting stuck," Obama said.

Republicans see ample room to take advantage of what they feel are weaknesses in Obamacare.

"I think it bodes really well for Republicans that the White House continues to deny reality. Unfortunately for the vulnerable running this year, President Obama can't unilaterally delay the November election like he has parts of Obamacare," Republican National Committee Chairman Reince Priebus told Reuters.

Problems with the president's healthcare law are part of a toxic mix as politicians must also grapple with Americans grousing about the job market and global instability presented by the Ukraine crisis.

"I think it's the lightning rod that sort of captures all the animosity and bad feelings that Americans have about everything else," said David Yepsen, director of the Paul Simon Public Policy Institute and Southern Illinois University. "Obamacare has come to symbolize something more than just healthcare. It's the general dissatisfaction that people have."

White House officials see Obama as a critical factor in emphasizing to Democrats the need to vote in elections in which his name will not be on the ballot. A prolific fundraiser, the president is in the midst of an active schedule of headlining events to raise money for Democratic candidates. His next event is in Miami on Thursday night.

Obama will help frame the debate around economic issues, they said, part of his drive to highlight the need to improve the quality of life for the middle class and fault Republicans for blocking his agenda.

While the White House is emphasizing the need for party unity, there is a recognition that some endangered Senate Democrats in more conservative states will put some distance between themselves and the president.

Democrats are in search of the best way to talk about Obamacare on the campaign trail.

A Democratic Party aide, speaking on the condition he not be identified by name, said Senate Democrats received a memo from pollster Geoff Garin in recent days alerting them of a poll taken in conjunction with this week's Florida special election.

The poll found that "keeping parts" of the Affordable Care Act that work and "fixing those that don't" drew higher numbers than "the Republican message of repeal," the aide said, adding that this is the message senators are urged to campaign on.

The aide said that "the potential larger issue is the president's unpopularity. If it doesn't improve, you may see more Senate Democrats shy away from him."

At a Senate Democratic retreat earlier this year, Obama said he understood why some Democrats do not want to campaign with him, and that he does not feel offended, said a Democratic senator asking not to be identified by name.

The president made clear he will campaign in those states where he can help rally support and get out the vote and will do what he can to raise campaign funds, the senator said.

Republicans need to pick up six Senate seats in order to wrest control of the 100-member chamber from Democrats. If they win the Senate, Republicans would control Congress, which would give them the ability to confound Obama's agenda for his remaining time in office.