WASHINGTON — President Trump has signaled in recent days that his closing pitch in this year's midterm elections is based on fear.

But while the presidential imprint adds to the weight of that message, warnings about dangerous outsiders, often with racially loaded images or language, have been coursing through key congressional races for weeks, including contests in the Philadelphia area.

In tight races in Bucks County and South Jersey, Republicans are running ads linking two Democratic House candidates to convicted cop-killer Mumia Abu-Jamal.

In one of those races, a GOP TV ad assailed Democrat Andy Kim as "not one of us" and a separate flier with a font styled like one from a stereotypical Asian take-out menu said there was "something fishy" about him. Kim, who grew up in South Jersey, is Korean American.

Elsewhere in the country, Republican ads have painted Democrats as terrorist sympathizers — one ad blared that a "Palestinian-Mexican millenial Democrat" is trying to "infiltrate" Congress. And the GOP candidate for governor in Florida has warned not to "monkey up" the strong economy by electing his Democratic opponent, who is black.

That was all before a caravan of some 7,000 Central American migrants moving toward the United States. became a focus for Trump. Without evidence, he warned the group is made up of violent gang members and "unknown Middle Easterners."

"Voters are motivated by fear and they're also motivated by anger," Trump ally Newt Gingrich told the Washington Post.

That's an old, but reliable, political truism. It's one reason why Republicans turned out in 2010, when Democrats held power and were pushing the Affordable Care Act, and why Democrats may have the advantage this year, in reaction to Trump.

Republicans have fewer reasons to be angry. They have been winning, and relatively few voters show up just to say "things are great, keep it up."

But the caravan, and dark warnings about terrorists, crime and "mobs" of liberal protesters, are aimed to counteract the Democratic intensity seen in many key races.

Some of Trump's recent statements have no grounding in evidence. Asked to explain his warnings about Middle Easterners Trump told reporters in the Oval Office Tuesday there's "no proof of anything but there could very well could be."

"This is one of his most dishonest weeks in political life," tweeted Toronto Star reporter Daniel Dale, who has fact-checked Trump throughout his presidency. "He's lying about so many different things at once, and in big ways — not exaggerating or stretching, completely making stuff up."

The liberal Huffington Post has a running list that includes racially charged claims in nearly two dozen campaigns. Others are based on wisp-thin connections.

U.S. Rep. Tom MacArthur (R., N.J.) has tried to tie Kim to Abu-Jamal because of a link to a book list posted on the Facebook page of a non-profit group Kim founded. The link, posted by a volunteer, not Kim, went to a separate site that listed more than 100 titles called "the Library of Resistance." Abu-Jamal's book was among them. Another Abu-Jamal-based attack, against Democratic candidate Scott Wallace, of Bucks County, was pulled because it lacked factual support.

In California, meanwhile, the GOP attack on the "Palestinian-Mexican" Democrat targets Ammar Campa-Najjar, whose grandfather had a role in planning the assassination of Israeli athletes at the 1972 Olympic Games, the New York Times reported. Campa-Najjar is a Christian who grew up in a Mexican American community and has distanced himself from that part of his family, the Times wrote.

Attack ads that push the boundaries and elicit fear, of course, are not new. But Trump has made loose accusations and racial tension central parts of his presidency, opening the door for others to follow.

"What Trump brought to the party has been so embraced that this is a Republican Party issue now, it is no longer just a Donald Trump issue," David Jolly, a former Republican congressman from Florida, told CNN Tuesday. He has left the party.

"The dog whistles of bigotry have been put away," tweeted U.S. Rep. Adam Schiff (D., Calif.). "Now they're using trumpets."

His tweet referred to the ads assailing Kim.

MacArthur, in response, noted that he didn't level the attack (it came from another Republican group) and that he has adopted two children from South Korea.

"I don't want your apology, but you sure can apologize to my children," MacArthur tweeted to Schiff.

Democrats have centered their closing arguments on health care and protections for people with pre-existing conditions, though Republicans have accused some, including Sen. Bob Casey (D., Pa.), of darkly painting GOP motives and exaggerating the threat.

Democrats point to the reality that Republicans have voted numerous times to repeal the Affordable Care Act, which includes protections for people with pre-existing conditions, or to weaken those protections.

Republicans, meanwhile, have been open about their strategy: As polls suggest independents and "soft" Republicans are uneasy with Trump, they hope to make Democratic candidates unacceptable alternatives.

What's unusual this year is that Trump and Republicans have a potentially positive message. They say the economy, jobs and wages are surging. But they're not emphasizing that argument in ads.

A Wesleyan Media Project report last week found that from Sept. 18 to Oct. 15, Republicans ads talked about taxes less often than they did in 2008, 2010 or 2012.

That's likely because the GOP tax plan, their signature legislative achievement, has fallen flat in public opinion polls. So the final weeks of the campaign feature talk about cop killers, gang members and dark warnings about migrants.