WASHINGTON – The caravan of Central Americans heading toward the United States is more than 1,000 miles from the border, but the political potency of their journey is already here.

President Donald Trump is increasingly seizing on the caravan as an issue in the midterm elections, hoping the images of migrants walking through Mexico will energize GOP voters in battleground states and potentially tip the balance in the fight for control of Congress.

"As we speak, the Democrat Party is openly encouraging caravan after caravan of illegal aliens to violate our laws and break into our country," Trump said at a rally Wednesday in Wisconsin, echoing a line he has used in recent days.

"The crisis on the border – and it is a crisis, it’s crazy – right now is the sole result of Democrat laws and activist Democrat judges that do whatever they want."

The thousands-strong group of migrants may also play into a fight expected to pick up immediately after the election: funding Trump's proposed border wall. The president and Republican leaders agreed to put off that debate until after the election, setting up an end-of-year showdown over a White House priority.

With the caravan grabbing headlines and border crossings on the rise, Trump may be able to convince wavering Republicans of the need for his wall.

“Millions of Americans are watching on television the thousands of immigrants tear open gates on their march to the U.S. border,” said Brian O. Walsh, president of America First Policies, a GOP fundraising group closely aligned with the president. “The ball is on the tee.”

Republican operatives – and Trump himself – have described the caravan as a political windfall, a symbol of a broken system they say is allowing the president to relitigate immigration as an issue that touches on the economy as well as law and order. Trump hit both themes hard during the 2016 presidential campaign.

The president has frequently invoked the caravan, estimated to include as many as 7,000 people, duringrallies over the past week. In addition to holding the migrants up as a symbol of ineffective policy, he has also sprinkled in claims that the group includes “unknown Middle Easterners” or that Democrats are funding the caravan.

Pressed by reporters for evidence of those claims, Trump said border agents regularly stop potential terrorists, before adding that “there’s no proof of anything.”

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Polling shows immigration remains a salient issue in several states holding important Senate races in next month's midterm election, including Arizona and Texas, and national surveys indicate the debate carries more weight with Republicans. The GOP is fighting to maintain its House and Senate majorities.

“This could be a blessing in disguise, because it's showing how bad our laws are,” Trump told USA TODAY in an interview this week as he flew to a rally in Houston, where he described the caravan as an “assault” on the country. “The Democrats are totally responsible.”

But GOP candidates are not unified on the president’s message about the caravan, and some have balked at the rhetoric he has used – noting it's not clear how many of the migrants are trying to enter the country illegally versus making an asylum claim. White House officials describe the asylum process as a "loophole" because immigrants are sometimes allowed to stay in the United States for months or years until their asylum claim is reviewed by a court.

Democrats speculate that Trump’s play for the base of the party may be turning off independent voters who are more circumspect about “zero tolerance” border policies.

“To emphasize … the criminals among them, I just don't think that it's the right way to approach it,” Sen. Jeff Flake, a retiring Arizona Republican and frequent Trump critic, told CNN on Tuesday.

Federal officials have in the past found that many of the migrants are entitled to an asylum review. Of 401 members of another caravan requesting asylum this year, 374 passed the first test, demonstrating that they have a “credible fear” of returning to their home country. Another 122 members of the caravan were apprehended trying to illegally enter the country.

More:A previous caravan faced the same federal scrutiny. Here is how that turned out

If the caravan is ginning up voter interest ahead of the midterms, it has yet to play a big role in campaign advertising. A USA TODAY review of Facebook ads in October showed only about four dozen ads mentioning the words “caravan” or “migrant.” Conservative groups predictably applauded Trump’s effort to “stop the illegal migrant caravan,” and liberal groups blasted the administration for its immigration policies.

By comparison, hundreds of political ads were placed by groups and candidates on Facebook in the days after the confirmation of Justice Brett Kavanaugh – another issue both parties say is energizing their voters.

The Trump administration faced criticism this year from Democrats and some Republicans for a “zero tolerance” strategy that forced the separation of thousands of children immigrants from their families. The White House ultimately reversed course, though some families are still being separated.

“Trump now wants to hold migrant kids in indefinite detention,” read one typical Facebook ad paid for by the liberal group MoveOn. “We must stop this cruelty.”

Karthik Ganapathy, a spokesman for the group, said the political debate has overlooked important context.

“The Beltway press has seen this as a play for base voters among the hard right that doesn’t carry any consequences for the left or the middle,” Ganapathy said. “We see it as kind of a desperate Hail Mary.”

'An issue created by Mr. Trump'

The growing caravan of Central Americans arrived in the southern Mexican town of Huixtla earlier this week. It began this month when a group of mostly Honduran migrants embarked on the trip.

Vice President Mike Pence said Tuesday that he spoke with Honduran President Juan Orlando Hernandez, who informed him that the caravan was "organized by leftist organizations and financed by Venezuela." He did not cite evidence to back the claim.

When Trump, sitting next to Pence in the Oval Office, interjected and teased Democratic senators that their party also had something to do with it, reporters pressed Trump for evidence.

"You know what? You're going to find out, and we're going to see," Trump said.

"Well, maybe they made a bad mistake, too. We're going to find out about that."

Explaining the president's earlier claim about “Middle Easterners” being mixed in with the caravan, Pence said border officials stop about 10 suspected terrorists a day from trying to enter the country. The statistic is likely based on a Department of Homeland Security memo that found agents encountered 2,554 people traveling to the U.S. in 2017 who had been placed on a terrorist watch list.

Most are stopped by agents working in international airports, not by agents stationed at ports of entry along the Southwest border.

Still, the White House has continued to describe the flow of immigrants as a "crisis." U.S. Customs and Border Patrol announced this week that the total number of apprehensions along the border for fiscal year 2018 rose to 396,579, a 30 percent increase compared with the previous year. Families and unaccompanied children made up nearly 40 percent of those apprehensions.

More:Tracking migrants: Caravan stops in small Mexican town on way to US border

More:Families and minors drive surge in migrant apprehensions at the Arizona border

After the election, Congress must decide whether to fund Trump's proposed border wall – a debate it has mostly punted on for two years. The timing will be even more pressing if Democrats capture control of the House, an outcome that would likely foreclose Trump's ability to get any wall money in his first term.

“Democrats are miscalculating things here,” said Shermichael Singleton, a Republican consultant. “The way the president has painted it, which I think is very smart, is that it’s about a lack of order, a lack of structure.

“When you think about conservativism as a philosophy, order is important, and structure is important.”

But some Democrats counter that the family separations are still raw enough for many that it will fire up their base as well.

The caravan "is not an issue that’s going to impact the lives of anyone in my district,” Democrat Jana Lynne Sanchez, who is running for an open House seat in Texas. “This only is an issue created by Mr. Trump to rile up his base.”

Contributing: David Agren, David Jackson, Susan Page