Doug Schoen, who was an adviser to former President Bill Clinton, warned House Democrats against reinforcing a “witch hunt” narrative that could help President Trump by launching a “sweeping” investigation into him.

In an op-ed Tuesday on FoxNews.com, Schoen wrote, “Ultimately, Congressional Democrats must be careful to proceed in a way that does not reinforce the “witch hunt” narrative that the president has perpetuated, and to not buttress his claims that the investigations encircling him are partisan and biased.”

House Democrats on Monday launched a demand from more than 80 people in Trump’s orbit, including his family, former Trump Organization employees, former campaign advisers, and former White House employees.

White House press secretary Sarah Sanders called it “a disgraceful and abusive investigation into tired, false allegations already investigated by the special counsel and committees in both Chambers of Congress.”

Sanders said in a statement:

Nadler and his fellow Democrats have embarked on this fishing expedition because they are terrified that their two-year false narrative of “Russia collusion” is crumbling. Their intimidation and abuse of American citizens is shameful. Democrats are harassing the President to distract from their radical agenda of making America a socialist country, killing babies after they’re born, and pushing a “green new deal” that would destroy jobs and bankrupt America.

Schoen said the investigation signaled that House Democrats were pursuing evidence that would become the basis of possible impeachment proceedings.

He cautioned Democrats that there was no “factual information released thus far” to build a bipartisan coalition for impeachment and advised them against doing anything before special counsel Robert Mueller’s investigation is complete.

He warned them not to let “partisanship” in their own investigations “taint or overshadow” Mueller’s investigation.

He also warned Democrats to “be mindful of how partisan-fueled impeachments have played out in the past,” given his experience working for Clinton. He wrote:

During my time working for President Bill Clinton, I witnessed first-hand what ensued when a Republican-controlled Congress politicized impeachment hearings. Not only was President Clinton not removed from office, but Democrats ended up winning reelection in 1998 with the slogan “Progress Not Partisanship,” which was in part inspired by my firm, and was a clear dig at congressional Republican’s partisan motives.

Ultimately, it would be playing into President Trump’s hands for the Democrats to pursue impeachment without unquestionable evidence of wrongdoing, he said.

He urged House Democrats to wait for Mueller’s investigation to conclude and to proceed with impeachment “only if” there is a “‘smoking gun’ that shows clear, unabashed, impeachable behavior or collusion.”

“I strongly urge Democrats to resist the urge to pursue impeachment in the absence of unquestioned evidence of wrongdoing, and to focus on the facts and only the facts. Doing anything else will only hurt the Democrats in 2020 and beyond,” he wrote.