The crisis at the southern border is surging as a top issue in states hundreds of miles away, allowing GOP Senate candidates the chance to capitalize in critical races in Ohio, Wisconsin, Michigan, Pennsylvania and Montana.

Why it matters: Immigration has long been one of Democrats' most vulnerable issues, but rarely has it found such traction outside of border areas. This year, the border crisis has become a top concern nationwide.

Driving the news: All three Ohio GOP Senate candidates — Matt Dolan, Bernie Moreno and Frank LaRose — have sought to outflank each other on the border as they battle to win Tuesday's primary.

• At a rally with former President Trump over the weekend, Moreno warned undocumented immigrants that "starting in January of 2025, you will be deported."
• The candidates have touted their visits to the border, repeatedly condemned the immigrant "invasion," urged construction of the border wall and floated using U.S. military force against Mexican drug cartels.

Zoom in: Sen. Sherrod Brown (D-Ohio), one of two red-state Democrats up for re-election, is a top Republican target.

• In a sign of immigration's significance in the race, Brown invited a county sheriff as his State of the Union guest after the two visited the southern border together.

By the numbers: Emerson polls over the past month have found immigration to be a top three issue for voters not only in the border state of Arizona, but also in Ohio and Pennsylvania.

• A plurality of Americans overall said immigration was the most important problem facing the U.S. — beating out government and the economy, according to Gallup polling last month.

Between the lines: The fentanyl crisis and cities' struggles to shelter and care for new immigrant arrivals have moved the border front and center in a new way.

• Hundreds of thousands of immigrants and asylum-seekers who recently crossed the border have been arriving in cities across the U.S. over the past year, aided by Texas' busing program.
• Local and state resources have been drained and tensions have escalated between Biden and state and local Democrats.
• Republicans' favorite issue has been given new potency in the very states they need to take control of the Senate.

What they're saying: "[E]very town in America from El Paso to New York City is a border town," National Republican Senatorial Committee Chair Sen. Steve Daines (R-Mont.) told Axios in a statement.

• "Every single Republican Senate candidate will spend the next eight months reminding voters of that fact," he added.
• "Republican Senate candidates lost their message on the border the minute they opposed the border security bill that was written by their own party," Democratic Senatorial Campaign Committee communications director David Bergstein said in a statement.

What to watch: Senate Republican candidates have seized on Democrats' history of downplaying the border issue or voting against border security measures.

• Wisconsin Senate candidate Eric Hovde routinely talks about a small college town in the state that has struggled to care for the roughly 1,000 immigrants who have arrived in recent years.
• The NRSC and Republican Senate candidate Tim Sheehy have already launched ads focused entirely on the southwest border and targeting vulnerable Sen. Jon Tester (D-Mont.).
• Pennsylvania Republican Dave McCormick's Senate campaign plans to zero in on the border issue, especially fentanyl trafficking.

The other side: The failure of the bipartisan border deal in the Senate at the hands of Republicans — spurred on by former President Trump — has given Democrats some breathing room and an opportunity to go on offense.

• "McCormick pretends to care about border security, but he said himself that he would have voted no on the bipartisan border deal," Sen. Bob Casey Jr. (D-Pa.) posted last month.
• Several Wisconsin swing voters in a focus group said they were upset by Trump's interference with the bill, Axios reported.
• Still, most said they thought Trump would do better at securing the border over Biden.