ST. LOUIS — In early February, abortion rights supporters gathered to change Missouri history at the Pageant — a storied club where rock ’n’ roll revolutionary Chuck Berry often had played: They launched a signature-gathering campaign to put a constitutional amendment to voters this year to legalize abortion in the state.

“We have fought long for this moment,” the Rev. Love Holt, the emcee, told the crowd. “Just two years after Missouri made abortion illegal in virtually all circumstances, the people of our state are going to forever protect abortion access in Missouri’s constitution.”

The ballot measure — which would allow abortions until fetal viability — outlasted 16 other related proposals and months of litigation with Republican state officials. Next, its supporters must gather more than 171,000 valid signatures by May 5.

Missouri is one of 13 states weighing abortion-related ballot measures, most of which would protect abortion rights. Abortion rights supporters hope to build on prior ballot wins in seven politically diverse states — California, Kansas, Kentucky, Michigan, Montana, Ohio, and Vermont — since the Supreme Court in 2022 overturned federal abortion protections, handing authority back to states.

In a presidential election year, national strategy also steers the money. The success of initiatives could hinge on a state’s relevance to broader party ambitions. Democrats are focused on where anger over the abortion rollback could propel voter turnout and spur party victories up and down the ballot, including in key races for the Senate and White House. Those wins would help guard against what Democrats see as a bigger threat: a national abortion ban.

Republicans are quieter about their national strategy around abortion. But at the state level, the groups mounting opposition campaigns are putting foot soldiers on the streets to deter people from signing ballot petitions.

Abortion rights supporters have raised millions more for ballot campaigns than have opponents, according to a California Healthline review of campaign finance records in multiple states.

Still, they “don’t have unlimited resources,” said Craig Burnett, an associate professor of political science at Hofstra University and expert on ballot initiatives. They must consider, “Where am I going to get the best bang for my buck here?”

Think Big America, a nonprofit founded by J.B. Pritzker, the billionaire Democratic governor of Illinois, is giving money to abortion rights initiatives in Arizona and Nevada and plans to do so in Montana, senior adviser Mike Ollen said. All are states where abortion remains legal to varying points in pregnancy, but each could have an outsize impact on the national political balance.

Arizona and Nevada are presidential swing states viewed as crucial for President Joe Biden to win reelection. They and Montana all have races that could flip control of the U.S. Senate from Democrats to Republicans in 2025.

Ollen said electoral consequences are “part of the calculus” for Think Big America. “We want to make sure that we protect abortion in the states that we’re going into,” Ollen said. “But we’re also not naive to the threat of a national abortion ban.”

About a fifth of key voter groups — Democratic women, women who live in states where abortion is banned, women who plan to vote for Biden, and women of reproductive age — identify as abortion voters, according to new polling from KFF.

Anti-abortion groups have pressured Republican candidates to support a national ban. Presumptive GOP presidential nominee Donald Trump quietly supports a 16-week ban with some exceptions, The New York Times reported.

Susan B. Anthony Pro-Life America, one of the nation’s largest anti-abortion groups, said it plans to spend “$92 million and reach 10 million voters” to back candidates in the political battleground states of Arizona, Georgia, Michigan, Montana, North Carolina, Ohio, Pennsylvania, and Wisconsin who would “protect life across America.” It will focus on “low turnout and persuadable voters to win the presidency and a majority in Congress.”

Ballot initiatives are one way for voters to assert their power over the political whims of state legislatures or courts. They are often viewed as more stable and harder to undo.

Abortion rights supporters must fend off statehouse maneuvers by Republicans to thwart ballot initiatives, such as proposals to change how ballot measures are approved or to buttress rules on collecting signatures. Politicians are appealing to the courts to beat back abortion rights.

In Montana, abortion is legally protected as a fundamental privacy right by a 1999 court ruling. Still, supporters are seeking to enshrine abortion access in the state constitution with a ballot measure.

Republican Attorney General Austin Knudsen, who has unsuccessfully asked the courts to overturn the 1999 precedent, rejected the draft initiative because it places “multiple distinct political choices into a single initiative.” The initiative’s backers, led by Planned Parenthood of Montana’s chief medical officer, Samuel Dickman, have asked the state Supreme Court to overturn Knudsen’s ruling and allow them to start gathering signatures.

Democrats hope the ballot question will drive voter turnout and boost reelection chances for incumbent U.S. Sen. Jon Tester against the likely Republican candidate, Tim Sheehy.

Tides Foundation, a social-justice-focused charity based in California, is monitoring ballot campaigns in Montana, Arizona, and Missouri, said Beth Huang, its program officer for civic engagement and democracy. It has granted funds in Florida and is in the process of approving funds for Colorado and Nevada, she said.

As a public charity, the group “legally cannot consider the partisan implications on any set of candidate elections” in funding decisions, she said. It will fund only ballot measures that would allow abortions at least until fetal viability — generally about 24 weeks — the standard under Roe v. Wade. A proposed initiative in Arkansas is off the table because access would go to 20 weeks.

“We are not interested in policies that do less than reestablish Roe,” Huang said.

In South Dakota, Dakotans for Health wants to reinstate abortion rights in the state. But an anti-abortion campaign says out-of-state money pays for signature drives that pressure people to sign the petitions without providing sufficient information on the measure. The Republican-dominated legislature passed a bill to let people remove their signatures from such ballot petitions. An emergency clause would put the bill into effect immediately if the governor signs it — ahead of the deadline to place the abortion question on the November ballot.

Critics of other states’ measures see other avenues for defeat.

Gregg Keller, a St. Louis-based Republican political strategist, said Missouri’s proposed amendment goes further than the measure passed last year in Ohio. For example, abortions could be allowed after fetal viability to protect the mental health of a pregnant person.

If opponents can get out the word that this goes further than what was done in Ohio and other states, “we have a chance of actually beating this thing,” Keller said. “If they are able to raise money. That’s a big if.”

Ballot supporters here raised $4.2 million as of March 12, according to campaign finance records. Money has come from national groups including the American Civil Liberties Union and the Fairness Project, which has supported ballot efforts on various progressive causes. Kansas City-based Health Forward Foundation has also donated.

So far opponents of the Missouri measure have raised $55,000, nearly half of which comes from the Catholic Church, according to campaign finance records.

“We went into this knowing that we were going to be outspent,” said Missouri Catholic Conference Executive Director Jamie Morris, who said he didn’t know whether the church would spend more. “We’re still going to be out trying to educate the faithful as best as we can, with the resources we have.”

Abortion Action Missouri Executive Director Mallory Schwarz said the coalition backing the state’s abortion measure is confident it will hit the signature goal by the May deadline.

If that happens, it will be up to outgoing Republican Gov. Mike Parson, who supports Missouri’s near-total abortion ban, to decide whether to put the measure before voters in the state’s August primary or the November general election.

Keller, the GOP strategist, said the governor will face tremendous pressure to put it on the August ballot. Five of six statewide offices are on the November ballot, as is Republican Josh Hawley’s U.S. Senate seat. An abortion ballot measure could overshadow those campaigns — just based on the war chests in play: Hawley’s 2018 campaign spent about $11.5 million, for example, while the three political action committees backing Ohio’s abortion amendment last year spent over $50 million.

“I am telling anyone who is running as a Republican this year that if you want to be able to make your case about how and why you deserve to be elected, and you want to be able to get your story out,” Keller said, “then clearly you would not want to have a $50 million ballot initiative on in November.”

KFF Health News rural health care correspondent Arielle Zionts and Mountain States editor Matt Volz contributed to this report.

This article was produced by KFF Health News, a national newsroom that produces in-depth journalism about health issues and is one of the core operating programs at KFF — the independent source for health policy research, polling, and journalism.