Some of President Trump’s biggest fans have declared war against special counsel Robert Mueller — and given Trump’s television-watching habits, he’s surely listening.

“Mueller is corrupt. The senior FBI is corrupt. The system is corrupt,” former House Speaker Newt Gingrich said on Fox News last week.

“A disgrace to the American justice system,” Fox News host Sean Hannity, a Trump favorite, declared. “The head of the snake.” Mueller has put the country “on the brink of becoming a banana republic,” he charged.

“Mueller poses an existential threat to the Trump presidency,” warned Christopher Ruddy, a longtime Trump friend who runs the conservative Newsmax website.

Even The Wall Street Journal published an editorial calling on the special counsel to quit. “Mueller is too conflicted to investigate the FBI and should step down in favor of someone more credible,” the newspaper argued.

Other conservatives, including members of Congress, have joined a chorus of complaints about the special counsel, the FBI and the Justice Department — even though all three are led by Trump appointees.

It all looks and sounds like a concerted campaign to delegitimize Mueller’s investigation, launched in May to look into evidence that Russia tampered with the 2016 U.S. presidential election.

Trump’s most fervent supporters disliked the idea from the start, but anti-Mueller fury stepped up markedly after the prosecutor indicted former national security advisor Michael Flynn this month. Flynn’s cooperation could enable Mueller to charge Trump with obstruction of justice, although there’s no sign that the prosecutor plans to take that step.

The anti-Mueller campaign isn’t just noisy; it’s dangerous. Gingrich, Hannity and Ruddy are people Trump listens to. Fox News is the channel he watches. Whether or not they persuade the president that he ought to fire Mueller, they are clearly paving the way — by convincing Trump’s political base, the Fox News-watching public, that dismissing the prosecutor would be justified.

But the case against Mueller is thin.

One major talking point is that although the special counsel is a Republican, many of the lawyers he has hired are Democrats. Six of Mueller’s top 15 aides donated money to Hillary Clinton’s campaign, according to Politifact; at least one gave to Republicans.

Critics have also complained that some of the FBI agents working on the investigation also worked on the 2016 investigation of Clinton’s emails, which they consider a whitewash. Among them, one agent has attracted particular attention: Peter Strzok, who was moved off the team by Mueller after he sent a derisive text message about Trump. GOP members of Congress are particularly angry that they didn’t learn about the incident until months later.

And they have charged that Mueller aide Andrew Weissmann, a career Justice Department official, is biased. The Wall Street Journal reported Friday that Weissmann attended Hillary Clinton’s election night party in November.

So, yes, the investigation — like every other part of the federal bureaucracy — includes Democrats. There’s no cure for that. Federal regulations prohibit the Justice Department from considering career appointees’ political affiliation.

That didn’t stop House Republicans from criticizing FBI Director Christopher Wray, another Trump appointee, when he appeared before them last week.

“If you kicked everybody off of Mueller’s team who was anti-Trump, I don’t think there’d be anyone left,” griped Rep. Jim Jordan (R-Ohio).

Trump’s lawyers say he’s never even considered firing the special counsel. But experts who worked on earlier investigations, both Republicans and Democrats, told me that Trump is essentially free to fire Mueller and, in effect, shut the inquest down — if he’s willing to take some political heat.

That doesn’t mean Mueller’s evidence will disappear. It will remain in the hands of the Justice Department. At that point, Congress can summon Mueller to disclose what he learned. Congress can also press for a new special counsel — or begin impeachment proceedings.

But Republican voters, primed by the delegitimization campaign, will press GOP senators and representatives to support Trump. Judging from the lawmakers’ performance so far, there’s little reason to expect that many would defy their most loyal voters.

Doyle McManus is a columnist for the Los Angeles Times.