WASHINGTON (Reuters) - U.S. President Donald Trump’s re-election campaign is countering impeachment efforts against him with a new surge in Facebook ads, while his Democratic rivals are saying little on the subject on the social media site or the campaign trail.

FILE PHOTO: U.S. President Donald Trump delivers remarks during a campaign rally at the Giant Center in Hershey, Pennsylvania, U.S., December 10, 2019. REUTERS/Tom Brenner/File Photo

Trump ran more than 2,500 ads mentioning “impeach” or “impeachment” in the week through Dec. 5, more than his campaign did in the prior two weeks combined, according to a Reuters analysis of data published by Facebook Inc.

The ads criticize the Democratic-led impeachment inquiry in the U.S. House of Representatives as producing “baseless LIES” and ask for money to support Trump’s bid to win another four-year term in November 2020.

The torrent of messages is a sign of Trump’s belief that the impeachment effort will backfire on Democrats, energizing his base and winning over independents skeptical of the process. Public opinion polls show support for impeachment is concentrated among Democrats.

Leading Democrats vying to challenge Trump next year have supported the impeachment process but ran only a handful of ads mentioning impeachment in recent weeks, according to the Reuters analysis of the most recent Facebook data available which was gathered by researchers at New York University’s Tandon School of Engineering.

They have focused instead on issues like healthcare, gun laws and climate change.

That could change if the Republican-led Senate takes up the impeachment matter next month and dismisses the charges, said Nicholas Valentino, a political scientist at the University of Michigan.

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“Dismissal will be a highly mobilizing tool” for Democrats, Valentino said.

House Democrats unveiled formal impeachment charges on Tuesday that accuse Trump of “betraying” the country by abusing power in an effort to pressure Ukraine to probe a political rival and then obstructing Congress’ investigation into the scandal.

While the House appears likely to approve impeachment, the Republican-controlled Senate is expected to dismiss the charges.

Trump has denied wrongdoing. He again ripped into Democrats at a campaign rally in Pennsylvania on Tuesday, calling the probe a hoax.

“The ONLY thing stopping Democrats from carrying out their impeachment WITCH HUNT is Patriotic Americans standing with President Trump,” according to the text of an ad Trump’s Facebook page ran on Dec. 3. Other anti-impeachment ads by Trump solicit supporters’ phone numbers and email addresses.

In contrast, Democrats’ recent Facebook ads have referred to impeachment only sparingly.

Massachusetts Senator Elizabeth Warren, a leading candidate for the Democratic nomination, mostly has focused her ads on strengthening gun laws, fighting corruption and raising taxes on wealthy Americans.

Her proposal for universal health insurance coverage was the key topic at a town hall in Las Vegas on Monday. Impeachment did not come up.

Former Vice President Joe Biden’s ads have focused on gun violence and his recent bus tour in early voting state Iowa. Biden launched new ads on Nov. 21 asking Facebook users to take a poll on whether Trump should be impeached.

Several Facebook ads for Pete Buttigieg, the mayor of South Bend, Indiana, who has been rising in polls in Iowa and New Hampshire, asked viewers to think about what he described as pressing issues.

“These big issues, from the economy to climate change, will not have taken a vacation during the impeachment process,” according to the text of three ads launched on Dec. 1.