Republicans and President Donald Trump were always going to use illegal immigration against opposition candidates in this year’s midterm elections — yet vulnerable Democrats likely did not think they would be hurt by the issue.

Trump is on the defensive, after all, on a variety of issues. And midterm elections can be brutal to the party with an incumbent in the White House.

But multiple immigration-related issues have hit one especially vulnerable Senate Democrat in Indiana in just the last few weeks. It seems increasingly evident that illegal immigration — Trump’s centerpiece issue — will be the hot topic of the 2018 election.

Last Sunday morning, a twice-deported Guatemalan national was driving drunk along Interstate Highway 70 in Indianapolis, and swerved into two men. Killed on impact were Edwin Jackson, an Indianapolis Colts linebacker, and the Uber driver he was trying to help, Jeffrey Monroe.

Donnelly also must deal with the fact that earlier this year, Indiana police arrested Huber Morales, 24, in the Evansville area for molesting a seven-year-old girl. Morales also reportedly gave the girl genital herpes. He said he was an illegal immigrant from Mexico.

“So disgraceful that a person illegally in our country killed Colts linebacker Edwin Jackson,” Trump tweeted Tuesday. “This is just one of many such preventable tragedies. We must get the Dems to get tough on the Border, and with illegal immigration, FAST!”

Democrats quickly reacted by attacking Trump. Marion County Prosecutor Terry Curry, a Democrat, criticized Trump Wednesday for his remarks, calling them “ghoulish,” and complained that Trump was forgetting two men were killed.

Curry filed four felony charges against Manuel Orrego-Savala, the Guatemalan citizen who had been deported in 2007 and 2009 (shown in the photo above left). But Curry’s swipe at Trump may be an attempt at political inoculation for Democrats. The Hoosier State will see one of the biggest races for the Senate — and it will involve freshman Sen. Joe Donnelly, a Democrat from South Bend (pictured above right).

Donnelly has numerous GOP rivals running first in the May 8 primary election. But they’ve already started attacking the incumbent Democrat for giving lip service to the issue of toughness on illegal immigration.

“Too often, Sen. Joe Donnelly tells Hoosiers one thing but does the opposite in D.C.,” Rep. Luke Messer (R-Ind.), a potential Donnelly rival, told LifeZette. Messer said the American people expect a wall along the southern border, a crackdown on sanctuary cities in the U.S., and a solution to illegal immigration in this country.

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Donnelly did not respond to LifeZette’s request for comment, but his official Twitter account included a statement on Jackson’s death. The senator said Orrego-Savala should never have been allowed to return to the United States after his 2007 deportation.

Related: Indianapolis Colts Player Killed by Twice-Deported Illegal Alien

Donnelly also claimed he had voted for “bipartisan” immigration reform, including border security. He was likely referring to the controversial “Gang of Eight” immigration bill of 2013 that passed the Senate but failed to get a vote on the House. That bill would have granted 11 million illegal immigrants a path to legal status, perhaps even citizenship.

Donnelly was elected in 2012. After the GOP nominated State Treasurer Richard Mourdock instead of aging incumbent Sen. Richard Lugar, Donnelly ended up narrowly winning. Also seeking to unseat Donnelly in 2018 is Rep. Todd Rokita. The primary election is May 8.

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Donnelly is among the most vulnerable of Senate Democrats up for re-election. A GOP win in Indiana would help Republicans keep their majority, which is presently only a 51-49 advantage. Democrats also must defend 25 of the 33 Senate seats that are on the ballot this year.

Of those 25 Democratic seats, five are in states where Trump beat former Secretary of State Hillary Clinton by double digits. In 2016, while Trump was taking Indiana by 19 points, Republican Rep. Todd Young beat a former Democratic senator, the once-invincible Evan Bayh, by 12 points.

The double whammy of shocking crimes committed by illegal aliens in Indiana has made for a potent political case against porous borders.

“I know the people, certainly in Indiana, are on the president’s side … This was a tragedy that could have been completely avoided.”

Rokita noted Tuesday night on Fox News that the federal government also filed charges against Orrego-Savala, but the previous administration of President Barack Obama released 20,000 such criminal aliens who collectively committed as many as 12,000 drunk-driving incidents in the U.S.

Rokita, speaking to “Fox News @ Night” host Shannon Bream, defended Trump from an attack by NFL star Reggie Bush, who claimed Trump’s immigration policies are racist.

“That’s just silly,” said Rokita. “I know the people, certainly in Indiana, are on the president’s side … This was a tragedy that could have been completely avoided.”

On the issue of tough border security, just how many people in Indiana and other key states are on Trump’s side will be something Donnelly and Democrats elsewhere will discover on Nov. 6, 2018, in the general election.

PoliZette White House writer Jim Stinson can be reached at [email protected]. Follow him on Twitter.