By Tim Reid

FORT DODGE, Iowa (Reuters) - Iowa resident Carolyn Miller had long harbored doubts about Joe Biden's candidacy, believing the former vice president was too old and too fumbling to beat President Donald Trump in November's election.

Then she saw Biden, 77, speak at a community college in Fort Dodge this week.

“Tonight clinched it for me. I didn’t find him old at all,” Miller, 78, said afterward. "We have to have him in there to straighten things out."

With less than two weeks before Iowa kicks off the Democratic nominating contest on Feb. 3, voters like Miller might explain Biden’s recent surge to the top of opinion polls there.

Beyond his name recognition as former President Barack Obama's No. 2 and the attention given to his bus tours across the farming state, Biden appears to be winning the electability argument with Democratic voters. They have increasingly cited beating Trump as their chief concern and consistently said Biden is the most likely candidate to do it.

Biden has seized on the latest crisis with Iran to tout his foreign policy credentials. He has also used the impeachment battle over Trump's effort to get Ukraine to investigate Biden to show his ability to weather attacks from a Republican president he argues fears him most as a competitor.

The turnaround for Biden, who trailed rivals Bernie Sanders, Elizabeth Warren and Pete Buttigieg in Iowa for much of the past year despite leading in national polls, is a promising sign for the front-runner who received less than 1% of the vote in the state during his failed 2008 bid.

Biden is now ahead or tied for the lead in Iowa with Sanders, a U.S. senator from Vermont. He has also risen into second place behind Sanders in polling averages in New Hampshire, the second state to vote in the nominating battle.

WINDOW OF OPPORTUNITY

A win for Biden in Iowa could upend the race. Unlike Warren and Buttigieg, who are banking on a strong showing in the predominantly white state to propel their campaigns forward, Biden has far stronger support from African-American voters in South Carolina and other more diverse states that could help him seal the nomination.

The contest remains extremely fluid and close among the top contenders. Biden also faces a threat from Michael Bloomberg, the billionaire former New York mayor who is spending millions of his fortune on his own White House campaign focused on later voting states.

Yet Biden's campaign has shifted from lowering expectations in Iowa to saying a win there would allow him to control the race from the start.

Trump's impeachment trial has given Biden another window of opportunity. Sanders and fellow Senators Warren and Amy Klobuchar – another Democratic contender - are now marooned in Washington six days a week serving as jurors during the Senate trial.

That left the moderate Biden with Iowa nearly to himself this past week.

In interviews with two dozen Iowans attending Biden's campaign events, Reuters found at least 12 who were undecided about Biden going in. On leaving, they all said Biden was now their pick.

“He won my vote. You can feel it in the room, his experience. The key is someone who can unite the country. People are sick of the fighting. And he’s ready to roll on day one,” Martin Lettow, 47, said after hearing Biden in Ames, Iowa.

A Biden campaign adviser said the plan had always been to have him spend more time with voters in intimate settings in the later stages of the campaign.

“He can really engage with voters on an emotional level, one-on-one,” the adviser said.

Karen Finney, a strategist who worked on Hillary Clinton's 2016 Democratic presidential campaign, said Biden's centrist positions and promise to work with foreign allies and Republicans at home to "restore the soul of the nation” resonated with voters in her recent focus groups.

“His message of healing the country – I can’t tell you how powerful that is," she said. "People are exhausted. He’s a calming force. I’m not sure voters are ready for big structural change."

HEAD VERSUS HEART

Speaking to campaign volunteers last week in Des Moines, Iowa, Biden clutched handwritten notes that included polling figures out that day showing him ahead in New Hampshire ahead of the state's Feb. 11 primary.

He regularly highlights his strength in polls, particularly those showing him as the Democrat best positioned to beat Trump.

Biden also tells crowds about his relationships with foreign leaders from his time as vice president and decades in the U.S. Senate.

He said the recent crisis with Iran, after Trump authorized the killing of top Iranian commander Qassem Soleimani in a drone strike on Jan. 3, revealed the president's dangerous and erratic foreign policy.

“There’s going to be no time for on-the-job training,” Biden said in Fort Dodge. The next president of the United States, Biden said, “needs to command the respect of the rest of the world."

The event was low-key, lacking the energy and excitement of the sort of rallies held by Sanders and Warren, two progressive candidates calling for fundamental changes to America’s economic and political systems.

But Vicki Tendall, 70, who said she had been anxious about a potential war with Iran, left convinced of Biden's ability to lead.

"Maybe we need someone older to do this,” she said.

Dennis Goldford, a political science professor at Drake University and an expert on the Iowa caucuses, said Biden "does not get the pulse beating fast." But in a year when Democratic voters are fixated on beating Trump, that might not matter.

“For Iowan voters, Biden is certainly the head rather than the heart,” Goldford said. “That’s the choice they are facing.”

(Reporting by Tim Reid; Editing by Colleen Jenkins and Peter Cooney)