WASHINGTON (AP) — A political shift is beginning to take hold across the U.S. as tens of thousands of suburban voters who helped fuel the Democratic Party's gains in recent years are becoming Republicans.

Across 31 states, about two-thirds of voters who have switched their official party registrations in the past year have switched to the Republican Party, according to voter registration data analyzed by The Associated Press. The phenomenon is playing out in virtually every region of the country — Democratic and Republican states along with cities and small towns — in the period since President Joe Biden replaced former President Donald Trump.

Nowhere is the shift more pronounced — and dangerous for Democrats — than in the suburbs. Over the last year, far more people are switching to the GOP across suburban counties from Denver to Pittsburgh. Republicans also gained ground in counties around medium-size cities such as Harrisburg, Pennsylvania; Raleigh, North Carolina; and Des Moines, Iowa.

Ben Smith, who lives in suburban Larimer County, Colorado, north of Denver, said he reluctantly registered as a Republican earlier in the year after becoming increasingly concerned about the Democrats' support in some localities for mandatory COVID-19 vaccines, the party's inability to quell violent crime and its frequent focus on racial justice.

"It's more so a rejection of the left than embracing the right," said Smith, a 37-year-old professional counselor whose transition away from the Democratic Party began five or six years ago when he registered as a libertarian.

The AP examined data from the 31 states in which voters explicitly register by political party and which make that information available to the public. Across those states, nearly 680,000 voters changed their registrations in the past year, according to L2, a political data firm.

While party switching is not uncommon, the data shows a definite reversal from the period while Trump was in office, when Democrats enjoyed a slight edge in the number of party switchers nationwide.

But over the last year, about 430,000 voters in those states shifted to the Republican Party, compared with about 240,000 who became Democrats. In another 12 states — including the electoral battlegrounds of Texas, Ohio and Virginia — L2 estimates each voter's party affiliation using records of voting in primary elections or statistical modeling. Those estimates, based on information such as demographics, local voting patterns and registered voter surveys, suggest that the same pattern is playing out in these states, too, with roughly two-thirds of voters whose affiliations changed in the past year moving toward the Republican Party.

The migration of hundreds of thousands of voters, a small portion of the overall U.S. electorate, does not ensure widespread Republican success in the November midterm elections, which will determine control of Congress and dozens of governorships. Democrats are hoping the Supreme Court's decision earlier this summer to overrule Roe v. Wade will energize supporters, particularly in the suburbs, ahead of the midterms.

Still, the details about party switchers present a warning for Democrats who were already concerned about the macro effects shaping the political landscape this fall.

Roughly four months before Election Day, Democrats have no clear strategy to address Biden's weak popularity and voters' overwhelming fear that the country is headed in the wrong direction with their party in charge. And while Republicans have offered few policy solutions of their own, the GOP has been working effectively to capitalize on the Democrats' shortcomings.

Republicans benefited last year as suburban parents grew increasingly frustrated by prolonged pandemic-related school closures. And as inflation intensified more recently, the Republican National Committee has been hosting voter registration events at gas stations in suburban areas across swing states like Arizona, Michigan, Nevada and Pennsylvania to link the Biden administration to record-high gas prices. The GOP has also linked the Democratic president to an ongoing baby formula shortage.

"Biden and Democrats are woefully out of touch with the American people, and that's why voters are flocking to the Republican Party in droves," RNC Chair Ronna McDaniel told the AP. She predicted that "American suburbs will trend red for cycles to come" because of "Biden's gas hike, the open border crisis, baby formula shortage and rising crime."

The Democratic National Committee declined to comment when asked about the recent surge in voters switching to the GOP.

And while Republican officials are quick to take credit for the shift, the phenomenon gained momentum shortly after Trump left the White House. Still, the specific reason or reasons for the shift remain unclear.

At least some of the newly registered Republicans are actually Democrats who crossed over to vote against Trump-backed candidates in GOP primaries. Such voters are likely to vote Democratic again this November.

But the scope and breadth of the party switching suggests something bigger at play.

Over the last year, nearly every state where voter registration records are available — even those without high-profile Republican primaries — moved in the same direction as voters by the thousands became Republicans.

In Iowa, Democrats used to hold the advantage in party changers by a 2-to-1 margin. That's flipped over the last year, with Republicans ahead by a similar amount.

In Florida, Republicans captured 58 percent of party switchers during those last years of the Trump era. Now, over the last year, they command 71 percent. And in Pennsylvania, the Republicans went from 58% to 63% of party changers.

The current advantage for Republicans among party changers is playing out with particular ferocity in the nation's suburbs.

The AP found that the Republican advantage was larger in suburban "fringe" counties, based on classifications from the Centers for Disease Control and Prevention, compared to smaller towns and counties. Republicans boosted their share of party changers in 91 of 133 suburban counties AP examined — 68% — over the last year, compared with the last years of the Trump era.

Republicans also gained ground in further-out suburban counties, which the CDC lumps in with medium-size cities and calls "medium metro" — more than 60% of such counties, 115 in all, saw Republican growth. They range from the suburban counties north of Denver, like Larimer, to Los Angeles-area ones like Ventura and Santa Barbara in California.

Some conservative leaders worry that the GOP's suburban gains will be limited if Republicans don't do a better job explaining to suburban voters what they stand for — instead of what they stand against.

Emily Seidel, who leads the Koch-backed grassroots organization Americans for Prosperity, said her network is seeing first-hand that suburban voters are distancing themselves from Democrats who represent "extreme policy positions."

"But that doesn't mean that they're ready to vote against those lawmakers either. Frankly, they're skeptical of both options that they have," Seidel said. "The lesson here: Candidates have to make their case, they have to give voters something to be for, not just something to be against."

Back in Larimer County, Colorado, 39-year-old homemaker Jessica Kroells says she can no longer vote for Democrats, despite being a reliable Democratic voter up until 2016.

There was not a single "aha moment" that convinced her to switch, but by 2020, she said the Democratic Party had "left me behind."

"The party itself is no longer Democrat, it's progressive socialism," she said, specifically condemning Biden's plan to eliminate billions of dollars in student debt.

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Peoples reported from New York.

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This story was first published on June 27, 2022. It was updated on July 7, 2022, to correct the number of voters who have switched from the Democratic Party to the GOP based on voter registration data. The initial story erroneously said voter registration data analyzed by the AP showed that more than 1 million voters across 43 states had switched to the Republican Party in the past 12 months. That figure was based on information about voters from the political data firm L2, and combined voter registration records with modeled information about the partisanship of voters in states without registration by party. The story should have been more clear about the distinction between the two types of information about voters.