Kari Lake, the leading Republican candidate for Senate in Arizona, was quick to denounce the state Supreme Court’s ruling upholding an 1864 law banning nearly all abortions in the state. The law is “out of step with Arizonans,” she said in a statement. She called on state lawmakers to “come up” with a “solution that Arizonans can support.”

But Ms. Lake, an ally of former President Donald J. Trump and a 2020 election denier, had voiced enthusiastic support for the law less than two years ago, when she was in the midst of a scorched-earth campaign for the Republican nomination for governor. Asked then what she thought of the ban, she said she was thrilled it existed and called a “great law.”

Asked for comment, the Lake campaign pointed to a post from Caroline Wren, a senior adviser to Ms. Lake, who insisted on Tuesday that Ms. Lake was not referring to the territorial-era law in the interview. But in that 2022 appearance, Ms. Lake cited the 1864 law’s number in the Arizona state code.

“I’m incredibly thrilled that we are going to have a great law that’s already on the books. I believe it’s ARS 13-3603,” she said in a 2022 interview on “The Conservative Circus With James T. Harris.” She made other remarks in support of the 1864 law during that campaign as well.

Ms. Lake’s retreat from the fervent anti-abortion rhetoric of her early 2022 campaign reflects the sharp changes in the politics of abortion in the nearly two years since the Supreme Court overturned Roe v. Wade, ending the constitutional right to abortion. Her shift also signals grave concern from Republicans, both in Arizona and across the country, that the issue will leave them electorally vulnerable in the fall — particularly in crucial battleground states like Arizona.

Republicans have been searching for a position that will shield them from the electoral blowback they have seen since Roe v. Wade was overturned.

But the revival of the 1864 law in Arizona amounts to something of a nightmare scenario for Republicans in the state. The Civil War-era law, which had laid dormant for decades, was enacted shortly after Arizona was organized as a remote frontier territory of less than 10,000 residents — and almost half a century before Arizona became a state and, months later, adopted women’s suffrage.

Starting in the 2022 midterms and in governors’ races, special elections and ballot measures, the abortion issue has helped Democrats notch victories across the country. And the Democratic Party is eager to push the issue to the front of this year’s races.

The White House said on Tuesday that Vice President Kamala Harris — who has focused on abortion rights on the campaign trail — would travel to Tucson, Ariz., on Friday to campaign on the issue. Last month, Ms. Harris met with abortion providers and staff members at a clinic in St. Paul, Minn., a striking political move that underscored Democrats’ new assertiveness on the issue.

Democrats, who had already seized on Mr. Trump’s new abortion stance on Monday, unleashed a salvo of fresh attacks after the Arizona ruling. They pointed to his latest statement that whatever states decide “must be the law of the land, and in this case, the law of the state,” as well as to his repeated boasting that he was responsible for ending Roe v. Wade.

The Democrats also trained their focus on Ms. Lake, posting other remarks from 2022, during which she expressed strict anti-abortion stances.

Ms. Lake, who is expected to win her primary, is likely to face Representative Ruben Gallego, a Democrat, in the fall, in a contest to determine the successor of Senator Kyrsten Sinema, who is not seeking re-election. Mr. Gallego’s campaign recently said it had raised $7.5 million in the first quarter.