ANCHORAGE, Alaska (AP) — An Alaska judge on Thursday refused to block a state investigation into whether Gov. Sarah Palin abused her power when she fired her public safety commissioner this summer.

Judge Peter Michalski threw out the lawsuit filed by five Republican state legislators who said the investigation had been tainted by partisan politics and was being manipulated to damage Palin shortly before the Nov. 4 presidential election.

"It is legitimately within the scope of the legislature's investigatory power to inquire into the circumstances surrounding the termination (of) a public officer the legislature had previously confirmed," the judge wrote in his decision.

The probe is looking into whether Palin, who is the Republican vice presidential candidate, and others pressured Public Safety Commissioner Walt Monegan to fire a state trooper who was involved in a contentious divorce from Palin's sister, and then fired Monegan when he wouldn't dismiss the trooper. Palin says Monegan was ousted over budget disagreements.

The five Republican lawmakers had argued that the legislative body that ordered the investigation exceeded its authority. Their attorney, Kevin Clarkson, said the political bias was demonstrated by the plan of the Legislature's independent investigator to issue a report by Oct. 10 although the full legislature won't consider until reconvening in January.

But Michalski said in his ruling that the mere appearance of impropriety does not mean any individual's right to fairness was violated.

The independent investigator, Steven Branchflower, still plans to conclude the probe and report his findings by Oct. 10, said Democratic state Sen. Hollis French, the investigation's project manager. Branchflower's report will not include the testimony of Palin's husband, Todd, and several top aides who refused to appear under subpoena.

In the ruling, released minutes before Palin and Sen. Joe Biden faced off in a debate in St. Louis, Michalski agreed with defense attorney Peter Maassen, who argued that the Legislature has the authority to investigate the governor as it sees fit.

"He agreed with us on pretty much everything," Maassen said of the judge's ruling. "The separation of power principles that governed this case seemed pretty clear."

Maassen represents the Legislative Council, 10 Republicans and four Democrats who authorized the investigation, and others involved in the probe.

Clarkson said in a statement that the judge's decision was "dangerous because it robs every Alaskan of the protection specifically provided by the Alaska Constitution" against bias interfering with due process.

At first, Palin agreed to cooperate with the probe, but since being picked Aug. 29 to be McCain's running mate, she, her family and staff have instead said the legislative investigation has been compromised by politics and that they would only cooperate with a separate investigation run by the Alaska State Personnel Board, whose members Palin can fire.

Michalski also threw out a lawsuit filed by Palin aides seeking to dismiss subpoenas compelling their testimony in the investigation. The aides had argued that the subpoenas should not have to be honored because they should not have been issued.

Todd Palin also refused to testify under subpoena, but he was not a plaintiff in the lawsuit filed by the state. His attorney, Thomas Van Flein, declined to say whether Palin would testify now, saying he had not seen the ruling to study the options.

"The question was never if Mr. Palin would testify, only where. The personnel board or the committee," Van Flein said by e-mail. "Now it could be both. But no decision has been made."