(CNN) — Six months ago, Republican voters were almost evenly split on whether special counsel Robert Mueller was conducting a fair investigation into potential links between President Donald Trump’s campaign and the Russian government.

Not anymore.

For the first time, a majority of Republican voters, 54%, now believe Mueller is not conducting a fair investigation, up 10 percentage points over the last six months, according to a new Quinnipiac University poll released this week.

Only 3 in 10 Republican voters, 30%, would say Mueller is conducting a fair probe into potential collusion, down 11 points over the last six months. Overall, however, a majority of American voters, 52%, believe Mueller’s probe is being conducted fairly.

The survey was conducted almost entirely before federal investigators on Monday raided the office and hotel room of the President’s lawyer, Michael Cohen. That day, Trump called the raid a “disgraceful situation” and “an attack on our country,” saying the investigation had reached a “whole new level of unfairness.”

Majorities of Democrats (82%) and independents (69%) — as well as Republicans (55%) — say the President should not fire Mueller.

Trump refused to rule out ousting Mueller from his post this week. “Well, I think it’s a disgrace what’s going on. We’ll see what happens. Many people have said you should fire him,” he responded to a question on dismissing the special counsel.

Lawmakers on both sides of the aisle, however, have warned against the President firing Mueller. Democrats across the board are pushing for legislation to protect Mueller, but Republican leadership has not signed on.

Still, Republican Sen. Chuck Grassley of Iowa told reporters this week that “it would be suicide” for Trump to remove Mueller from his post and GOP Sens. Lindsey Graham of South Carolina and Jeff Flake of Arizona have previously called the move an impeachable offense.

The Quinnipiac University poll was conducted April 6-9 among 1,181 registered voters nationwide. The margin of error is ±3.4 percentage points for the full sample; it is larger for subgroups.

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