It was midway through a three-day swing of Iowa for Mike Pence when Luann Bertrand confronted him at a Pizza Ranch.Ms. Bertrand, a retired store manager whose family also farms corn and raises cattle outside Sioux City, had a question about Jan. 6, 2021, the date that looms under the Pence campaign like a land mine.Mr. Pence took questions from voters at a meet-and-greet at Pizza Ranch, a chain restaurant in Sioux City. Luann Bertrand, a retired store manager whose family also farms corn and raises cattle outside Sioux City, was among them.Jesse Brothers/Sioux City Journal, via Associated PressIn Iowa, the state whose caucuses next year are make-or-break for Mr. Pence, Ms. Bertrand accused the former vice president of putting President Biden in the White House. Seated at a table of G.O.P. voters in the restaurant, Ms. Bertrand, dressed in gray, shook a finger at Mr. Pence as she told him he should have rejected the electoral votes of certain states on Jan. 6.Mr. Pence, after listening with hands clutching his belt, offered a forceful rebuttal.A Question for Mike Pence“If it wasn’t for your vote, we would not have Joe Biden in the White House. Joe Biden shouldn’t be there. And all those wonderful things you and Trump were doing together would be continuing, and this country would be on the right path. Do you ever second-guess yourself? That was a constitutional right that you had to send those votes back to the states. It was not like you were going to personally elect him. We all know by the number of votes that were there who won that election. You changed history for this country.”The SubtextFor a former vice president, Mr. Pence holds a position in the Republican presidential race that is both credibly strong and incredibly weak: He ranks third in polling averages, but with only about 7 percent support, far behind former President Donald J. Trump and Gov. Ron DeSantis of Florida.Digging into the polls suggests why: About one in three potential Republican primary voters views Mr. Pence unfavorably. In a survey of registered voters nationwide, the same share says they would never vote for him.Anti-Trump Republicans are wary of Mr. Pence’s years of quiet servitude as the No. 2, while much of the G.O.P. base that embraces Mr. Trump and his continued lying about the 2020 election blames Mr. Pence for his actions on Jan. 6, when he refused to block certification of the results.Mike Pence’s Answer“The Constitution affords no authority to the vice president or anyone else to reject votes or return votes to the states. It had never been done before. It should never be done in the future. I’m sorry, ma’am, but that’s actually what the Constitution says. No vice president in American history ever asserted the authority that you have been convinced that I had. I want to tell you, with all due respect — I’ve said it before, I say it right now — that President Trump was wrong about my authority that day, and he’s still wrong.”The SubtextMr. Pence is not running a race focused on Jan. 6; he presents himself as a traditional conservative in the Ronald Reagan mold. Still, the exchange was a crucial moment for Mr. Pence, in the eyes of the candidate, his campaign, a super PAC that supports him and outside Republican strategists.What Other People Are SayingDevin O’Malley, a spokesman for the campaign, said it was the first time a voter openly queried Mr. Pence about “sending back” 2020 electoral votes to state legislatures, a common fallacy on the right. Mr. Pence decided to lean into his response to make a statement, Mr. O’Malley said.“I don’t think the moment was lost on him that the answer that he gave was going to be one that was kind of the answer of record and would be given a lot of attention.“We view it as an opportunity to set ourselves apart from other candidates. On the issue of who stands firmly with the Constitution of the United States under immense pressure, I don’t think there’s a moment in recent history that any one political leader has faced which has put on display their character and their judgment more than that one day.”On Friday, Mr. Pence returns to Iowa with other Republican candidates (but not Mr. Trump) for the Family Leadership Summit, a gathering of evangelical voters. These voters make up the most crucial bloc for Mr. Pence’s candidacy, but they retain a strong allegiance to Mr. Trump.Bob Vander Plaats, president of the Family Leader, the group sponsoring the summit, said Mr. Pence did the right thing by tackling Jan. 6 head-on in Sioux City, though there are many voters he might never bring around.“He has to own it and double down on it. Everybody’s got their hurdle, and this is going to be one that Mike Pence is going to have to clear.”“Because the former president has boastfully said Pence was wrong and he wimped out and he lacked courage, his base of supporters are going to believe that. Pence is not going to win that issue with Trump’s base. But Pence isn’t trying to win Trump’s base.”Scott Reed, co-chairman of a super PAC working to elect Mr. Pence through grass-roots organizing and advertising in Iowa, agreed. To him, Mr. Pence’s response to the voter was golden. “We put it in the can,” he said, meaning that the tape will show up in a future television ad.“There’s a segment of the party that we’re never going to get — the Steve Bannon crowd. And there’s plenty of the party left for us to get.”David Oman, a longtime center-right Republican strategist in Iowa who is unaffiliated with a campaign, said it was unclear whether Mr. Pence’s rebuttal of the voter — and his swipe at Mr. Trump — would help in the caucuses, which are Jan. 15, 2024.“Will it be helpful or unhelpful in six months? We’ll see.”“My personal view is history will be good to Mike Pence with respect to what happened on Jan. 6. Someday he’ll get the Presidential Medal of Freedom. Probably from a Democratic president.”What the Voter SaysIn a follow-up interview, Ms. Bertrand, the voter who challenged Mr. Pence, repeated a falsehood that lawyers who told Mr. Trump that his vice president could refuse states’ electoral votes had won prior cases for Mr. Trump.(The Trump lawyer who advanced that fringe theory about the 2020 election, John Eastman, is facing disbarment in California. Mr. Pence’s legal advisers told him that Mr. Eastman was wrong, and one testified before a grand jury investigating Mr. Trump over the Jan. 6 riot.)Although Ms. Bertrand was a Trump supporter in 2020, she is uncertain whether she will back him in the caucuses next year and said she wanted to hear from other candidates. Mr. Pence, however, failed to convince her that he acted correctly on Jan. 6.“President Trump has been accused time and again and went to court and won every case, and so I’m under the assumption that in this case, when President Trump said he had a right to challenge Pence on his decision, it was his lawyers that told him that — the same lawyers who had come out on top before.”“But if I am right or I am wrong is not important. To me, the idea Pence needs to know is there are people in Iowa — and I think in the entire country — that still believe this. That’s a challenge he’s up against when he’s running.”“I did not feel that I was personally attacking him. I just wanted him to know, hey, there’s more of me than of you out there.” More