Pennsylvania’s race for governor takes on huge stakes for abortion rights.

Now that the Supreme Court has struck down Roe v. Wade, the most important election this year in America when it comes to abortion will be the contest for governor of Pennsylvania.

Josh Shapiro, the state’s Democratic attorney general, is facing off against Doug Mastriano, a Republican state senator who has vowed to make abortion illegal. If Mr. Mastriano wins, the Republican-controlled Pennsylvania legislature is all but certain to move to undo the state’s existing law allowing abortion.

“The stakes in this governor’s race could not be more clear,” Mr. Shapiro said Friday. “The contrast between me and my dangerous opponent could not be greater.”

Nowhere else is a governor’s race so pivotal. In Wisconsin, where the Republican-led Legislature has battled with Gov. Tony Evers, a Democrat who is seeking re-election, a pre-Roe law forbidding abortion automatically went back into effect after Friday’s decision. Mr. Evers has pledged to fight for abortion rights, but he faces a wall of opposition from Republican state legislators.

This week, Mr. Evers ordered Wisconsin’s lawmakers to the State Capitol in Madison for a special session meant to reverse an 1849 law outlawing abortion. Republicans ended the session on Wednesday without taking action.

In Michigan, Gov. Gretchen Whitmer, a Democrat, has backed a series of creative legal arguments to block the state’s 1931 law outlawing abortion from taking effect. In May, a state judge ruled that the law would not immediately go into effect after an eventual Supreme Court ruling on Roe.

Ms. Whitmer has also supported an effort to place a referendum on the November ballot to enshrine abortion rights in Michigan’s Constitution.

Three other states will have questions about abortion decided directly by voters in November.

Kansas and Kentucky have referendums asking voters to affirm that their state constitutions do not guarantee a right to abortion. In Vermont, the ballot will contain a question that would enshrine a person’s right to control their own reproductive choices in the state’s Constitution.

Gov. Laura Kelly of Kansas, a Democrat who supports abortion rights, faces a difficult re-election bid. Her likely Republican opponent, Derek Schmidt, the state’s attorney general, opposes abortion rights.

Democratic governors on Friday cast the Supreme Court’s decision as a catastrophic move — and the first step toward a broader rollback of women’s rights.

“Right now it’s abortion they are taking away,” Gov. J.B. Pritzker of Illinois said at a news conference in Chicago. “They are allowing states to criminalize the exercise of reproductive rights.”

Mr. Pritzker, who is seeking a second term in November, said Illinois would be “a safe haven” for women from across the country. He called on the state’s General Assembly, controlled by Democrats, to convene a special session to further enshrine abortion rights in Illinois.

Three Democratic governors on the West Coast — Govs. Gavin Newsom of California, Kate Brown of Oregon and Jay Inslee of Washington State — on Friday announced a consortium to maintain abortion access. Of the three, only Mr. Newsom faces re-election in November, in a race he is heavily favored to win. Ms. Brown is prohibited by term limits from running again, and Mr. Inslee was re-elected in 2020.

Democratic candidates for governor in states with Republican-controlled legislatures like Georgia, Arizona and Texas said they would fight for abortion rights if elected — though in practice there is little they could do toward that goal given Republican opposition.

“I will work with the legislature to reverse the draconian law that will now rule our state,” said Stacey Abrams, the Democrat running for governor of Georgia.

In Maine, where Democrats now control the Legislature, Gov. Janet Mills said on Friday that “my veto pen will stand in the way” of any legislative effort to restrict abortion rights if Republicans took power.

And in Minnesota, Gov. Tim Walz, a Democrat, said his office was now “the last line of defense against an abortion ban in Minnesota,” though control of the state’s Legislature is split between Democrats and Republicans.

Republican governors sought to press a political advantage as well. In Virginia, Gov. Glenn Youngkin told The Washington Post on Friday that he would seek a ban on abortion after 15 weeks — though such a move is unlikely to be successful given that Democrats control the State Senate. Virginia’s next round of state legislature elections won’t take place until 2023; Mr. Youngkin, who took office in January, is prohibited from seeking a second consecutive term.