Donald Trump is helping increase Republican turnout virtually everywhere he competes, including in traditional battleground states he’d need to win to become president.

The real estate mogul routinely brags about booming participation in primaries and caucuses as evidence he's bringing new voters to the party. His opponents dismiss that explanation, saying the big field of candidates and resulting media attention have been the main propellants.

While no single cause can completely explain the trend, the result is inarguable. A Bloomberg Politics analysis of county-level data shows voter participation has more than doubled in many areas—including in portions of swing states Ohio, Florida, Iowa, New Hampshire and Nevada—compared with similarly timed, competitive contests in 2012.

"The question for Trump is, will the additional voters he brings into the party—mostly white men and those with less than a college degree—offset the almost certain ground he will lose among millennials, Hispanics and, likely, independent-women," said John Della Volpe, polling director at the Harvard Institute of Politics.

If Trump wins the Republican nomination, white, working-class voters could give him a boost in some crucial general election states. Ohio, Pennsylvania, Wisconsin, Michigan and Iowa, have higher proportions of those voters than more demographically diverse battleground states in the southern and western U.S.

"Will the new and lapsed Trump voter stay motivated until November, even if he softens some rhetoric'' for broader appeal? Della Volpe asked. "I don't know, but these are the likely questions that his campaign is struggling with now."

The billionaire’s ability to expand voter participation will be tested again today as he competes in Arizona and Utah, two states that both have voted Republican in 11 of the last 12 presidential elections.

Ohio’s Mahoning County, which includes Youngstown and other areas still wounded by steel plant closures in the 1970s and early 1980s, is one of the more dramatic examples of the primary turnout boost in a battleground state.

“We were stunned on election night looking at those numbers,” said Mark Munroe, the county’s Republican Party chairman. “The Trump factor was the primary driver.”

There were 34,503 ballots cast there in last week’s Republican primary, up 125 percent from four years earlier when Mitt Romney, Rick Santorum, Newt Gingrich and Ron Paul were competing for the nomination. Trump won the county, trouncing Ohio Governor John Kasich, 50.6 percent to 37.4 percent.

Munroe, who supports Kasich, said Democrats and independents “crossing over to vote for Trump” accounted for the bulk of the increased activity. He bases that on the number of phone calls he received from non-Republicans before the primary asking him how they could vote Republican, with some wanting to support Trump and others wanting to block him.

The night before the Ohio primary, Trump appeared near Youngstown, where he blasted Kasich for supporting the North America Free Trade Agreement when he was a member of Congress. Many blame the accord, which took effect in 1994, for the area’s lost manufacturing jobs.

Through the first 12 primaries held this year, the nonpartisan Pew Research Center found that Republican participation is on a record-setting pace, with the combined turnout of 17.3 percent of eligible voters being the highest of any year since at least 1980. The analysis didn’t include caucus states.

The trend for higher Republican turnout started with the very first contest this year, the Iowa caucuses. Participation shattered records and was up almost 54 percent from 2012.

While nomination contests can’t predict what will happen in a general election, they can reveal demographic pockets of support for candidates. In 2008, then-Senator Barack Obama attracted a higher-than-usual primary turnout among black voters, a trend that carried over into the general election.

“That told us something about Barack Obama’s candidacy for the general elections,” said William Frey, a senior demographer at the Washington-based Brookings Institution. “It said that there was a groundswell there and it continued.”

If Trump does manage to win the Republican nomination, he can’t bank on the added turnout during the primaries to boost him to victory in a general election. In the six instances that Democrats and Republicans both had competitive primaries since 1976, PolitiFact found that the party that drew more votes in nomination contests also got more votes just three times in the general elections that followed.

After his win in Florida and three other primaries last week, Trump argued that he's expanding the size of the Republican electorate and that the party forces opposing him should instead rally behind him.

"We have a great opportunity," he said. "Democrats are coming in. Independents are coming in, and, very, very importantly, people that never voted before."

The data on Trump's claim about who is turning out is murky. In Florida’s primary, 22 percent of those who voted on the Republican side were independents, up from 18 percent in 2012, exit polling showed.

Trump also can’t fairly claim all the credit for heightened Republican voting. The once huge Republican field, the massive media coverage the race has received and the fact that party activists eager to reclaim the White House after seven years of Democratic control are almost certainly contributing factors.

Ed Goeas, a Republican strategist who is part of an anti-Trump effort, said Friday on Bloomberg Politics’ “With all Due Respect” program that the front-runner is getting too much credit for the increased turnout.

“These are general election voters that tend not to participate in primaries,” he said. “It’s not like he’s bringing huge numbers of people to register to vote for the first time.”

Florida's Seminole County is another example of a place where turnout was well above 2012 levels. The bedroom community northeast of Orlando saw roughly 62,000 people cast Republican ballots in last week's primary, up 28 percent from four years ago.

Trump won the county with almost 42 percent of the vote on his way to winning Florida's 99 delegates and ending the campaign of home-state Senator Marco Rubio.

Seminole was among the 66 (out of 67) counties the businessman won in Florida. The county tilts slightly Republican in general elections and Romney, the 2012 nominee, won 52.6 percent of the vote there in 2012.

Candidates often visit the county because it’s part of the “I-4 corridor” that follows an interstate highway stretching from Tampa Bay to Orlando to Daytona Beach. The area often decides whether statewide elections in Florida are won or lost.

“That means we received a lot of candidate attention,” said Mike Ertel, the county’s supervisor of elections. “It draws activity with people going to the polls and voting.”

The Republican turnout increases defy easy geographic explanation, with states from blue Massachusetts to deep-red Mississippi recording them, the Bloomberg analysis shows.

The uptick is especially strong in southern states. One county in Alabama—Choctaw—recorded a 424 percent increase from the March 2012 primary.

The county, in southwest Alabama, saw the biggest jump in turnout among the more than 800 counties included in the analysis from 13 states that had primaries in both the first quarter of 2012 and 2016.

In 2012, just 409 people turned out for the Republican primary, a small fraction of the 2,143 who did on March 1. Trump easily won the county with 49.9 percent of the vote.

Like many of the counties where Trump has done well, Choctaw County has faced economic challenges, including the textile industry's move out of the U.S. The racially mixed county had an unemployment rate of 9.5 percent in January, well above the national average of 4.9 percent.

—With assistance from Greg Giroux in Washington