Mr. Buttigieg, the South Bend, Ind., mayor who shot to prominence in the spring but has since slipped back, has determined that while television news and many in the political class focus on impeachment, he has a shot at trying to organize his way to a top-tier finis h in the Iowa caucuses on Feb. 3.

Thanks to a nearly $25 million fund-raising bounty in the spring, which he topped up with a respectable $19.1 million over the summer, as reported Tuesday, Mr. Buttigieg has been able to invest in a gold-plated ground game in Iowa as he seeks to challenge two candidates who have been organizing for longer here, Senators Elizabeth Warren and Bernie Sanders .

“We’re entering the stage where the rubber meets the road,” Mr. Buttigieg said in an interview as his four-day trip wrapped up last week. “ In order to settle the question of electability , the best thing you can do is perform well in an actual election. Iowa’s of course the first. And so that’s where a lot of our focus is going to go.”

Grass-roots organizing is essential to a strong caucus finish. Word of mouth about a candidate is often what turns people out on a cold February night. The Buttigieg campaign, which opened its bus tour to live-tweeting journalists in an effort to set itself apart, is also road-testing a somewhat novel approach to organizing. Its Iowa volunteers first contact friends and family members rather than cold-calling lists of registered voters, who are now so bombarded they ignore unknown numbers.