WASHINGTON — In a mail piece that reads as if it could have been spoken or tweeted by President Trump himself, Rep. Lou Barletta of Pennsylvania declares that "America is at war" with "violent criminal aliens" flooding the country.

Barletta, a longtime hard-liner on illegal immigration, is the leading Republican seeking to challenge Democratic Sen. Bob Casey in Pennsylvania. His mailer shows how Trump's rhetorical style on a signature issue has filtered down to fellow Republicans, experts said. Democrats call it extremism.

"With every day that passes more Americans are killed or victimized – whether by violent criminal aliens who are untouchable within the 'Sanctuary Cities' of the left," the mailing continues, "or by radical terrorists who sneak across our border or walk right through the front door via liberal schemes like the 'Diversity Visa Lottery Program.' "

It also touts Trump's personal praise for Barletta, uses the phrase America is at war three times, and says that in response the congressman is seeking to build a conservative "army."

"You mobilize through fear, and this is a rhetoric based on fear," said Kathleen Hall Jamieson, an expert on political communication — although she added it can backfire if it spreads beyond the intended audience.

A few years ago, this kind of language would have been limited to the most extreme voices or direct-mail advertising that couldn't be directly tied to a candidate, particularly when it came to someone running in a swing state like Pennsylvania, said Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania.

Trump has changed that.

"There's nothing in there that isn't consistent with what President Trump has said as president or as a candidate," said Jamieson, "It's now been normalized. … This is a person who is signaling identity with Donald Trump."

Indeed, Barletta rose to prominence by taking a firm stand on illegal immigration as the mayor of Hazleton and then by vocally backing Trump in 2016.

He stood by the letter — but in defending it used narrower framing.

"I believe we're at war with drug dealers here in America, with illegal drugs coming into the country," Barletta said in an interview Thursday. "Yes, I believe we're at war with gang members who are recruiting our children, 9 and 10 years old."

The mailing did not use such specific language, although it did single out "terrorism."

Republicans, including Trump, have emphasized individual cases of illegal immigrants who have been accused of terrorism or serious crimes, like rape and murder, blaming immigration policies and "sanctuary city" rules, like those in Philadelphia.

Federal statistics and several studies by groups that favor immigration have concluded that immigrants, including undocumented immigrants, are less likely to commit crimes than native-born Americans, although there is debate about some of the studies' methods.

"I never say that everyone that comes into the country illegally is a terrorist, criminal drug dealer, gang member," Barletta said in the interview. "What I'm saying is: If I gave you 10 grapes and two of them had poison in it — how many grapes would you eat?"

Max Steele, a spokesman for the Pennsylvania Democratic Party, called the mailing the work of "a desperate, extremist candidate."

"Rather than working to find common ground and actually reform our immigration system, Barletta is doing what he always does: stoking fear and grandstanding," Steele said in a statement.

Terry Madonna, a pollster at Franklin & Marshall College, noted that Barletta needs to improve his fund-raising to show national Republican groups that his race is worth investing in. The letter seeks donations of up to $2,700, the maximum allowed for an individual.

"I've seen some strongly worded fund-raisers. This goes to the top of the list," Madonna said. "They recognize they are trailing in fund-raising and this is a major appeal at a critical moment in the debate over immigration."

Barletta had $1.1 million on hand as of his latest report and raised less than $500,000 in the last quarter of 2017. Casey had $8.7 million.

Madonna said he expects Barletta to make immigration a central piece of the campaign.

On Thursday, Barletta attacked Casey for voting against a proposal from Sen. Pat Toomey (R., Pa.) to withhold some federal funding from so-called sanctuary cities like Philadelphia, where local police do not aid deportation efforts or detain suspects longer than they otherwise would based on their immigration status.

"Bob Casey is thumbing his nose at the rule of law and putting Americans last," Barletta said in a statement after Toomey's bill was blocked.

Casey noted that he supported a bipartisan immigration bill in 2013 that offered both tougher border security and a path to citizenship for undocumented immigrants.

"There would be no sanctuary cities if Republicans in Congress would enact comprehensive immigration reform," Casey said in a statement, adding that "anyone who commits a violent crime should go to prison, no matter who they are."

Immigration proved potent for Trump in 2016, although Toomey took a narrower approach as he won reelection, targeting sanctuary cities while generally avoiding harsher rhetoric about the issue overall.