“The numbers indicate that our party has been more successful than we previously knew in getting voters of color moving to the GOP,’’ said Neil Newhouse, a veteran pollster who led polling for several GOP presidential nominees. “Ever since I got involved in politics more than 40 years ago, that’s been a long-term goal of the party.”

The voter shifts helped Republicans win a majority of House votes nationally, preliminary results show, but weren’t strong enough to bring the party substantial gains in House seats. Republicans have so far lost a net of one seat in the Senate, with the final tally to be decided in Georgia’s runoff election next month. Still, the gain among these groups “tells me that Republicans are potentially well-positioned to win a national election, if we can replicate this,’’ Mr. Newhouse said.

Ruy Teixeira, a demographer at the American Enterprise Institute, a conservative think tank, said the shift among Latino voters was particularly noteworthy and extends a move toward the GOP that was a feature of the last two presidential elections. “They lost quite a bit among Latinos, and the swing was significant,” he said.

Many caveats apply in drawing lessons from a midterm election. Far fewer voters participate than in a presidential contest. The voter shifts detected by AP VoteCast varied widely by state and by whether an election had the potential to restrict legalized abortion. Voters’ choices this year might have been driven more by their views of former President

Donald Trump

and of candidates who copied his style of politics, than by their views of the two parties. Mr. Trump is now a declared candidate for the GOP presidential nomination in 2024.

The AP VoteCast survey, which included more than 94,000 midterm voters nationwide, found a number of significant shifts in voter preferences:

—Latino voters favored Democratic House candidates by 17 percentage points—giving 56% support to Democrats and 39% to Republicans—a far slimmer lead than the 28-point edge that helped President Biden win in 2020 or the 34-point Democratic advantage in the last midterm elections, in 2018.

—Black voters gave 14% of their support to GOP House candidates, compared with 8% in the elections of two and four years ago.

—White women with college degrees, who had backed Democrats by 19 points in the last midterms and by 21 points in the 2020 presidential election, tipped toward Democrats by a far narrower 6 points this year.

—Republicans won an outright majority of white women in the suburbs, carrying the group by 6 percentage points. Suburban white women had backed Mr. Biden by 5 points, and Democratic House candidates in 2018 by 7 points. Female voters overall, who account for over half the electorate, favored Democrats by a single percentage point, down from 12 points and 15 points in the last two elections, respectively.

Some Democrats cautioned that little could be read into results from a midterm election with special conditions. The fate of legalized abortion was a pressing issue in some states, which helped Democratic candidates, and was less salient in others.

“I’m skeptical, because it wasn’t a national presidential election, and because you have such differences state by state,’’ said Elaine Kamarck, a veteran of the Clinton administration White House who is now a senior fellow at the Brookings Institution.

Analysts said that more data were needed to better understand what the variations among voter groups from state to state meant to the election outcomes. Some early clues suggest that the Latino voter shift boosted the GOP vote share in some House races, even if the shift didn’t produce a victory.

In some Latino-rich House districts in California, Democratic candidates won their elections with far smaller vote margins than the party produced two years earlier. Rep.

Norma Torres

of Southern California, for example, won by 12 points in preliminary results in a district that Mr. Biden carried by 28 points.

Republicans cut into Democratic margins in two heavily Latino House districts in South Texas. Democratic Rep.

Vicente Gonzalez

won re-election by 8 points in a district that Mr. Biden had carried by 15 points, while Republican Monica De La Cruz won in a newly created district by 9 points, which Mr. Trump had carried by 3 points.

In a third South Texas House district, Democratic Rep.

Henry Cuellar

won re-election by a larger margin than Mr. Biden won in 2020.

Carlos Odio, co-founder of Equis Research, a Democratic-aligned firm that focuses on Latino voters, said the Hispanic vote varied significantly by state.

“Florida was an unmitigated disaster for Democrats across the board. But it is especially true among Latino voters,’’ he said. Republicans won a majority of the Hispanic vote for the first time since 2006, Mr. Odio said. Republicans carried heavily Latino Miami-Dade County, the state’s largest, “something that was unthinkable in the Obama era,’’ he said.

Republicans boosted their share of voters who don’t have a four-year college degree. They also dominated among white voters in rural areas and small towns, winning a commanding 70% of those voters—producing an advantage of about 40 points—compared with leads of about 30 points two years and four years ago.

The AP VoteCast survey was conducted by NORC at the University of Chicago for The Wall Street Journal, the Associated Press and Fox News.

Write to Aaron Zitner at aaron.zitner@wsj.com and Anthony DeBarros at Anthony.Debarros@wsj.com