The abortion battleground in the US has moved to states and their new efforts to restrict abortion or strengthen protections following the report of a leaked majority draft opinion by the Supreme Court that indicated it is prepared to overturn the federal right to abortion.

Politico's publishing of the leaked draft on Monday also rallied Democrats and Republicans for the November midterm elections, but especially Democrats, as they seek to mobilize voters and avoid predicted steep losses in Congress and statehouses.

Democratic Illinois Governor J.B. Pritzker predicted "a tsunami of activism" among Democratic voters ahead of the midterms. "People thought this was settled law," he said. "Now they are this morning awakened. Now reproductive rights and women's rights are the number one issue and they are on the ballot."

The draft obtained by Politico says the 1973 case Roe v. Wade "was egregiously wrong from the start", and it would strike it down, eliminating the constitutional right to abortion. States still would be allowed to provide abortions, according to the draft.

Some 22 states already have antiabortion laws that could go into effect if the landmark case is overturned, and political leaders in other states on Tuesday and Wednesday quickly reacted to the draft opinion.

Republican South Dakota Governor Kristi Noem tweeted Tuesday that she would immediately call for a special session "to save lives and guarantee that every unborn child has a right to life in South Dakota".

In Alabama, a Republican legislative leader promised quick action "to quickly end abortion within our border".

Supreme Court Chief Justice John Roberts said in a statement that the published draft opinion was authentic but wasn't necessarily the final resolution of the court's decision on Roe. The decision isn't expected until summer, when the court's term concludes. Roberts also said an investigation has been launched to determine how the draft was leaked.

Democratic governors in New York and California on Tuesday said they would seek amendments to their state constitutions to strengthen laws that protect abortion rights.

California's state Senate also is considering a bill that would create a government fund to help pay for abortions, including for residents from states where the procedure is restricted or outlawed.

Connecticut Governor Ned Lamont, a Democrat, on Tuesday reaffirmed his commitment to sign a bill into law that would reinforce abortion protections in the state. The bill also would expand the type of practitioners eligible to perform certain abortion-related care.

Democratic governors of Oregon, Washington and Colorado didn't propose new measures but reiterated their support to keep abortion legal in their states.

The governors of Massachusetts, Vermont and New Hampshire, who are among the few Republican leaders who support abortion rights, echoed the Democratic governors' support for abortion. A state constitutional amendment affirming the right to abortion is on the ballot in Vermont for November.

Some Republicans want Congress to enact a national ban on abortion, but Democrats currently control both chambers of Congress by narrow majorities.

While Democrats on Capitol Hill expressed outrage at the draft opinion, they acknowledged that their hands are tied unless voters give them a strong majority in Congress this fall. The Senate is narrowly controlled by Democrats, and there aren't enough senators who support abortion rights to overcome a filibuster or to create a 51-vote majority.

"A lot of what the Biden administration could do would be window dressing, in that ultimately we're going to have a system of conflicting access to reproductive health and rights depending upon the state you live in," said Lawrence Gostin, director of the O'Neill Institute for National and Global Health Law at Georgetown Law, who has been advising the White House on its options. "And there's very little that [President Joe] Biden can do about that," he told The Washington Post.

Minnesota Democratic Senator Tina Smith said, "The reality is that we have to organize, and we have to win elections. If we win and we have a majority in the Senate that we can work with, then we can talk about issues like the filibuster and other steps that we can take to reclaim the courts."

Public opinion polls show that while most Americans support some restrictions to abortion, a majority have consistently opposed overturning Roe for decades.