TRENTON -- Gov. Chris Christie's job approval rating sank to a new low, according to a poll that shows it slipping from 26 percent in June to 21 percent in October.

Seventy-two percent of registered voters, including 52 percent of Republicans surveyed, said they disapprove of the Republican governor is doing in the Garden State, a Fairleigh Dickinson University PublicMind poll released Wednesday found.

The poll declared these the worst approval and disapproval ratings for Christie "ever."

"Apparently we've not yet found the floor for the governor's approval among voters in the state," said PublicMind Director Krista Jenkins.

Jenkins suggested the governor has been tarnished by the ongoing George Washington Bridge lane closure scandal trial, in which a former Port Authority executive and Christie's one-time deputy chief of staff are accused of shutting down several local toll lanes as an act of political retribution.

Christie likely also lost some Republican support by agreeing to raise the gasoline tax 23 cents a gallon to raise money for the depleted Transportation Trust Fund. Though Christie said it is the first and only tax increase he will sign -- and it was accompanied by $1.4 billion in tax cuts -- Jenkins said that "no doubt caused some in his party to turn against him."

On Bridgegate, more than half of voters, 52 percent, said "sufficient proof" existed that Christie was aware of the lane closure scheme and did nothing to intervene.

The governor has denied knowing anything about the lane shutdowns before they happened or the efforts to cover up.

Fifty-seven percent of Republicans, compared with just 18 percent of Democrats, said there is not enough proof that Christie was in on it.

Thirty-one percent said it was "very unlikely" that he knew.

"The Bridgegate trial and its fallout is clearly hurting the governor. With both sides arguing that the governor was aware of the political retaliation plan, voters are having a hard time coming up with reasons to believe his claims of innocence," Jenkins said.

Still, the majority of voters, 57 percent, said Christie should remain in office. Just 39 percent said that he should either step down on his own or be removed. Democrats, 58 percent, were more likely than Republicans, 38 percent, to say that he should resign or be impeached.

"Invoking the word 'impeachment' raises his early departure to a different level," Jenkins said. "Although removal by impeachment has been discussed recently in the press, it's clear from these numbers that the public is not ready to go there, despite growing concerns about the veracity of the governor's claims regarding his role in the lane closure affair."

PublicMind surveyed 848 registered voters from Oct. 12-16. It has a margin of error of plus or minus 3.6 percentage points.

Samantha Marcus may be reached at smarcus@njadvancemedia.com. Follow her on Twitter @samanthamarcus. Find NJ.com Politics on Facebook.