George Soros, a major Democratic donor, has become a frequent target of ads on Facebook by conservative groups and Republican organizations. (Facebook/Facebook)

President Trump alleged last week that George Soros is paying people to protest at his rallies. A top executive at Campbell Soup tweeted that Soros was helping thousands of Central American migrants head in a caravan to the United States. The county clerk in Texas’s Harris County has warned that Soros wants to control local elections.

The 88-year-old billionaire hedge fund founder, one of the country’s biggest Democratic donors and long a target of the right, has been the subject of escalating political attacks in the run-up to Election Day. On Facebook, several conservative groups — including the GOP House campaign committee — are running ads that feature Soros as a boogeyman, according to a review of political ad data released by the social media company.

The charged rhetoric is drawing renewed criticism after Soros was among a group of prominent figures on the left targeted this week with homemade explosive devices.

“America’s political leadership is stoking the fires of hate and unleashing a climate that tolerates violence and racism,” said Laura Silber, spokeswoman for Soros’s Open Society Foundations. “They are setting the tone at the highest offices. We are calling for restoring a level of civility and respect for other people’s opinions.”

In response to a request for comment, a White House spokesman referred to a tweet by press secretary Sarah Sanders, in which she called the attempted bombings “despicable” and said “anyone responsible will be held accountable to the fullest extent of the law.”

Trump said Wednesday that “we have to come together” and send the message that “threats of political violence of any kind have no place in the United States of America.”

Soros, who could not be reached for comment, told The Washington Post in a June interview that he was unfazed by efforts to demonize him.

“I’m proud of my enemies,” he said.

Many of the attacks on Soros have been fueled by his lengthy history of extensive political spending on behalf of liberal causes and candidates. Since 2010, he has plowed $39 million into super PACs aligned with Democrats, campaign finance records show.

This cycle, he has donated $13.2 million so far to independent groups active in federal elections, including Priorities USA Action, a major Democratic super PAC; Win Justice, which focuses on voter turnout in battleground states; and Senate Majority PAC, which is aligned with Senate Democrats.

In addition to his political giving, Soros’s Open Society Foundations is slated to spend about $1 billion this year promoting free speech and other issues in 100 countries, pouring much of his fortune into promoting liberal values and fighting a rising tide of nationalism, including in the United States. The nonprofit spends $150 million domestically, some of which helps funds groups such as Planned Parenthood and the American Civil Liberties Union.

Critics on the right — including the president — have stoked the image of Soros as an all-powerful financier, often claiming without evidence that he is responsible for grass-roots activities on the left.

In Washington, he was blamed for the protests that erupted over the nomination of Brett M. Kavanaugh to the Supreme Court. In Harris County, Tex., County Clerk Stan Stanart claims on his campaign website that Soros wants to control local elections — a statement he has left up even after acknowledging it was based on unfounded rumor, the Houston Chronicle reported.

In an interview with The Post on Wednesday, Stanart — whose office oversees voting in Houston and the surrounding county — said it was “a very strong rumor” and “there are grounds for saying Soros meddles in Harris County politics.”

“Is he doing it now, I don’t know,” he acknowledged. “I haven’t had time to go back and update my website.”

Trump has increasingly made references to Soros’s power, alleging during an Oct. 18 rally in Missoula, Mont., that people holding up signs for Democrats are “paid by Soros or somebody, right?” He said in an Oct. 11 interview with Fox News that “the Democrats and Soros” paid for protesters at prior rallies.

On Facebook, Soros figures prominently in ads paid for by conservative organizations and GOP committees, according to an archive of politically themed ads posted online by the social media company.

One of the biggest efforts is by Judicial Watch, a conservative group that is raising funds through a campaign it calls “Expose Soros.” One of its Facebook ads featured a black-and-white photo of Soros circled in red.

Tom Fitton, president of Judicial Watch, said in an interview that he is investigating whether U.S. taxpayer funds have backed Soros’s agenda. He said he saw nothing wrong with highlighting Soros to help raise money for his group.

“This is not unusual for folks like Mr. Soros to rise in terms of public consciousness, especially because he is one of the biggest supporters of hard-left activism here and abroad,” Fitton said, adding that the bombing attempts would not affect his group’s campaign.

“We will continue to investigate the intersection between the government and George Soros operations,” he said.

House GOP leaders have also used Soros as a central figure in their midterm messaging.

In an ad posted on Twitter on Tuesday night, House Majority Leader Kevin McCarthy of California said in a video that Soros is one of three people funding the Democratic Party, along with hedge fund founder Tom Steyer and former New York mayor Michael Bloomberg.

“We cannot allow Soros, Steyer and Bloomberg to BUY this election!” McCarthy tweeted.

Matt Sparks, a spokesman for McCarthy, said that “the video simply points out the enormous financial contributions a select few have made in this year’s midterm campaigns. Any suggestion that content condones or incites violence is wrong.”

Some of the harshest attacks on Soros this cycle have come from the National Republican Congressional Committee. One of committee’s video ads attacks a Democratic candidate for the House from Minnesota, Dan Feehan, an Iraq War veteran. The ad seeks to tie Feehan to “billionaire George Soros” who “bankrolls the resistance.” It shows Feehan wearing a badge that says he is “paid for by George Soros.” The video concludes with a picture of Soros and Feehan amid blazing fires.

The NRCC released another ad Wednesday, which accused Feehan of being tied to the “radical George Soros.”

Sean Oyaas, Feehan’s campaign manager, said in a statement that “these dishonest attacks are exactly what Minnesotans are tired of and represent a broken Washington.”

A spokesman for the NRCC did not respond to a request for comment.

A Facebook ad sponsored by Liberty Nation, a conservative website, shows two hands with puppet strings under the headline claiming Soros and Steyer were part of “the radical left out to buy Florida.”

Liberty Nation did not immediately respond to a request for comment.

Steyer — whose staff stepped up security this week after the threats to Soros and other figures on the left — said in an interview Wednesday that he understands there are criticisms and risks involved with being a large donor.

“If you’re trying to tell the truth and you’re trying to stick up for the American people and do the right thing and people criticize you for it, you’ve got to ignore them,” he said.

On Monday, a vice president of government affairs of Campbell Soup, Kelly Johnston, tweeted a conspiracy theory that Soros’s Open Society Foundations sent “troop carriers” to support a caravan of migrants from Central America headed to the United States. He said that Soros’s group “planned and is executing this, including where they defecate.”

Campbell Soup said in a statement that Johnston’s comment does not represent the company’s position. Tom Hushen, a company spokesman, said Johnston was not available for comment.

The broadsides against Soros come amid intensifying threats of violence against figures across the political spectrum. Conservatives such as the Koch brothers and Kavanaugh have been targeted with death threats.

Soros, a Holocaust survivor and self-described agnostic Jew, has long been subject to anti-Semitic attacks and even allegations that he collaborated with the Nazis.

In the final days of the 2016 race, Trump spoke in his closing television ad about sending a tough message to “global special interests” who wanted to control Washington, as images of Soros and other financial leaders who are Jewish flashed on the screen amid footage of Clinton.

Earlier this year, the actress Roseanne Barr tweeted that Soros is “a nazi who turned in his fellow Jews to be murdered in German concentration camps & stole their wealth.”

Barr’s message was retweeted by the president’s son, Donald Trump Jr.

In his interview with The Post, Soros said the allegation that he was a Nazi collaborator were “a total fabrication.” Soros has said he used false papers at age 13 to survive the Nazi occupation of Hungary.

Barr later apologized for her tweet and said Soros “was persecuted by the Nazis.”

Democrats on Wednesday criticized Trump and other Republicans for what they called incendiary comments about Soros.

“The slurs against George Soros that Republicans continue to invoke are dredged up from centuries of nauseating anti-Semitism,” Rep. Bill Pascrell Jr., (D-N.J.), said in a statement. “They have helped create an environment that has fostered all this.”

One of Soros’s sons, Alexander, wrote in an op-ed in the New York Times on Wednesday that the rhetoric against his father “got worse” as a result of Trump’s presidential campaign, citing the ad that included an image of Soros. “A genie was let out of the bottle, which may take generations to put back in,” the younger Soros wrote.

Michelle Ye Hee Lee, Anu Narayanswamy, Andrew Tran and Dave Weigel contributed to this report.