Democratic U.S. Sen. Al Franken raised $12 million in preparation for what is expected to be a tough fight to keep the seat he barely won six years ago.

Fundraising figures released Friday show Franken had nearly $5 million left as he started the year. Mike McFadden, so far his best-funded Republican rival, posted an impressive cash haul for a first-time candidate: $2.2 million, with $1.7 million left on hand.

"Our best way to fight back and make sure that Senator Franken can keep fighting for the middle class is to have the funds we need," said Franken campaign manager Matt Burgess.

Campaign finance totals reported Friday to the Federal Election Commission starkly show the power of incumbents to garner cash.

U.S. Rep. Erik Paulsen, a Republican in Minnesota's politically diverse suburban Third District, had $1.7 million on hand at the end of 2013 and no major challengers.

GOP Rep. John Kline, of the south suburban Second Congressional District, started the year with $1.6 million in the bank. Kline will face a challenger in next week's Republican caucuses and, if he prevails, a Democratic opponent in the fall. Neither of his rivals posted figures close to Kline's.

Democratic U.S. Rep. Collin Peterson, who said this week he would decide in March whether he will run again, raised money last year as if he had already made up his mind for re-election. He brought in half a million dollars last year and had $360,000 left over to run again in his Republican-leaning western Minnesota district. Those figures are in line with what he has raised in ­previous election cycles. His Republican challenger, Torrey Westrom, brought in $84,000 in December, when he joined the race, and spent very little of it.

As experienced members of Congress, the four incumbents can use their resources and their connections to continue to tap political money.

Franken may have a strong lead in the cash race, but Republicans believe they have a far better shot of toppling him than they had of ousting Democratic U.S. Sen. Amy Klobuchar two years ago. Republican candidates will begin their first true faceoff as Minnesotans go to precinct caucuses Feb. 4.

McFadden is a businessman making his first run for elected office. "I'm running because of Minnesotans like this young man who lost his insurance," he told supporters earlier this week. "Obamacare has to go, and so does Al Franken."

Among the other Republican candidates, Chris Dahlberg, a St. Louis County commissioner, raised about $100,000 and had spent about half of it. GOP state lawmakers Julianne Ortman and Jim Abeler did not release ­fundraising figures on Friday. Ortman staffer Jim Sanborn said the campaign would wait to release any details and Abeler did not return a call requesting the figures.

Unlike House candidates, Senate candidates file on paper, which means it takes weeks for their fundraising figures to become easily accessible.

Late Friday, Dahlberg said it was "unfair to the people who will be participating in precinct caucuses" not to have fundraising information available as they make their decisions at next week's caucuses.

Eighth is competitive

Only in the Eighth Congressional ­District did a challenger begin to approach the figures posted by an incumbent. In that district, Democratic U.S. Rep. Rick Nolan raised $563,000 last year and had almost $300,000 left on hand. Republican Stewart Mills, of the Mills Fleet Farm family business, raised $450,000 and had more than $306,000 left, besting Nolan's cash-on-hand figure.

In recent elections, the northern Eighth District has flipped from Democratic control to Republican hands and back to Democrats again. While nonpartisan political handicappers give Nolan an advantage, Republicans see the Eighth District as their best chance to take a Minnesota seat from the DFL if Peterson, a Democrat in a largely Republican district, does not retire.

In several other U.S. House races, candidates who hope to join Congress for the first time boosted their fundraising by putting in their own money.

GOP primary in the First

In southern Minnesota's First Congressional District, Republican Aaron Miller lent his campaign $40,000. Miller is vying against Mike Benson and Jim Hagedorn in a GOP contest to take on Democratic U.S. Rep. Tim Walz. Walz had nearly $300,000 left after his 2013 fundraising haul of $640,000. None of the Republican candidates had even a quarter of that amount.

Several candidates in the heated race to take Republican Michele Bachmann's place in the Sixth Congressional District also used their own cash to ­bolster their fundraising. Republican Rhonda Sivarajah used $150,000 in personal funds last year to reach her $213,000 total haul. She had most of her money still left to spend. Competitor Phil Krinkie lent his campaign $300,000 last summer. His year-end fundraising figures were not available Friday evening.

In that race, Republican Tom Emmer led the pack. A former state representative who ­narrowly lost the race for governor in 2010, Emmer took in $626,000 total last year and had $335,000 left to spend. Emmer is considered the GOP's front-runner in that race.

"I continue to be grateful for all the support and backing I have for my campaign," Emmer said.

Rachel E. Stassen-Berger Twitter: @RachelSB