Al Ameling, 58, a technical analyst who lives in Marble Rock, near the Minnesota border, is representative of the profound demographic shift among white rural voters in the northern Midwest that helped produce Mr. Trump’s stunning upset. Mr. Ameling voted for Mr. Obama in 2008, sat out in 2012 and enthusiastically backed Mr. Trump. Nothing he has heard since Election Day has shaken his support, including reports this week that American intelligence agencies are investigating unverified accounts of meetings between Trump aides and Russian officials, as well as sex tapes purportedly made of Mr. Trump in Moscow. On Wednesday, Mr. Trump called the allegations completely false.

“The way it is nowadays, unless I see positive proof, it’s all a lie,” Mr. Ameling said in a telephone interview on Wednesday. He added he was more concerned that government officials might have leaked the material to the news media. “I don’t know if it was classified, but if it was, whoever leaked it needs to go to jail,” he said. “We need law and order back in this country.”

I headed to Monticello because it was the site of Hillary Clinton’s first campaign stop after declaring her candidacy for the Democratic nomination in 2015. When she rolled up in her black van, a pack of journalists took off at a run, myself included, an enduringly silly image.

Mrs. Clinton rarely returned to the state in the general election campaign, giving it up as all but lost. Jones County, which includes Monticello, is the birthplace of the painter Grant Wood, and where older men still wear the style of pinstriped overalls in his “American Gothic.” It is a beautiful place, with bald eagles soaring over wintry farm fields. Mr. Trump carried the county by 20 percentage points; Mr. Obama easily won there four years earlier.

At Darrell’s, there are actually two Tables of Knowledge, one favored by Democrats and the other by Republicans. Among them are an optometrist, farmers and former employees of a utility company. I asked if there was anyone who had voted for Mr. Trump after having previously supported Mr. Obama.