WASHINGTON - With no election of his own this year, U.S. Sen. Al Franken has spent many a weekend crisscrossing the country to support Democratic Senate candidates in too-close-to-call races.

The battle for control of the Senate has intensified this fall as tight races in battleground states across the country, including Wisconsin, are stoking concern among Democrats and boosting Republican hopes.

With Senate Democrats clinging to a slim majority in the upper chamber, Franken has played a crucial role as celebrity fundraiser, lending his name and time for events from Connecticut to California.

Franken has headlined fundraisers for Senate candidates or state Democratic parties in 15 states and has directly donated nearly $300,000 to candidates, parties and the Democratic Senatorial Campaign Committee, which works to elect Democrats to the U.S. Senate.

With an eye toward 2014, Franken has also quietly jump-started his own campaign: A full two years before voters head to the polls, the first-term senator has raised $3.3 million for his re-election bid.

"Senator Franken has been one of the most effective advocates for Democratic candidates across the country, inspiring tremendous enthusiasm among supporters," said Guy Cecil, executive director of the senatorial campaign committee. "I absolutely think that will help put him in a strong position when he's up for re-election."

Franken's star power has made him a money magnet that draws crowds wherever he lands, said University of Minnesota political scientist Kathryn Pearson.

"That's not much of a surprise," said Minnesota Republican Party Chairman Pat Shortridge. "He's something of a national liberal celebrity and people will reap the benefits of that."

Critics such as Shortridge say Franken is cleverly padding his own election coffers and résumé ahead of 2014, all while scoring points with the fellow Democrats he may need to rely on two years from now. Franken said he is more concerned about populating Congress with like-minded candidates who support Democratic principles than getting a head start on re-election.

With Minnesota's senior senator, Amy Klobuchar, comfortably ahead in the polls against her Republican challenger Kurt Bills, Franken said he has more time to rally supporters and raise dollars in battleground states such as Nevada, Ohio and Virginia.

He also is personally connected to many of the candidates he's stumping for. Montana Sen. Jon Tester lent key staff support to him during his 2008 Senate campaign, and Franken returned the favor this year. During Franken's days as a radio talk show host, Massachusetts Senate hopeful Elizabeth Warren was a frequent guest and he's now helping her race against Republican Sen. Scott Brown.

Franken funnels most of the donations through his Midwest Values political action committee, which he created in 2005 to support liberal candidates.

"All these people share my progressive values," Franken said.

To take control of the Senate, Republicans would have to pick up four seats if President Obama is re-elected.

If Republican presidential nominee Mitt Romney wins, Republicans would have to pick up three because Paul Ryan, as Romney's vice president, would serve as the Senate's tiebreaking vote.

"We need to hold the Senate," Franken told a crowd in Massachusetts last month. "We do know that, and that is within your control."

A Democratically controlled Senate would prevent a total Republican takeover of Capitol Hill and the White House if Romney wins the presidential race and Republicans retain their majority in the U.S. House.

In the event that Democrats are swept out of power, Franken said, the future of several programs will be threatened: federal health care reform, Medicare, the Head Start program for low-income families and Pell Grants for college students among them.

In 2008 Franken was locked in a tight, costly election battle with former U.S. Sen. Norm Coleman, and a third-party candidate, that stretched well beyond Election Day with recounts and legal challenges. The race cost more than $40 million and Franken won with less than 42 percent of the vote.

His stock appears to have risen since then. A Star Tribune Minnesota Poll conducted in September shows that he now has a 52 percent approval rating among likely voters -- his best showing in a publicly released poll.

"He's been able to overcome some critics that didn't know if he would be able to serve as a serious legislator," Pearson said.

The poll results didn't impress Shortridge, who said Franken should expect another tough race in 2014 now that he has a record his opponent will be able to dissect.

Citing Franken's support of Obama's federal stimulus program and Affordable Care Act, Shortridge said Franken has "supported policies that knocked this country off track and frustrated Minnesotans."

Franken said his focus is squarely on representing Minnesota, even when he's not there.

"You are looking at a senator who won by 312 votes," Franken told the Massachusetts crowd last month. "My charge to you is 'Work your butts off.'"

It's advice he plans to follow.

"Even though this race could be every bit as close as mine," he wrote to supporters Thursday in a fundraising e-mail for Nevada Senate candidate Shelley Berkley, "I don't plan to go to bed until I find out if [she] is coming to fight alongside me in the Senate."

Corey Mitchell is a correspondent in the Star Tribune Washington Bureau. Twitter: @CMitchellStrib