Sen. Scott Bundgaard is scheduled to take the witness stand today in what has become the biggest fight of his political life.

The Peoria Republican, who is accused of violating Senate ethics rules and could be expelled from office, is expected to give a vigorous defense of his actions during a Feb. 25 scuffle with his then-girlfriend.

He is expected to reiterate what he has before — that he was merely trying to protect Aubry Ballard, whom he said had threatened to get out of the car as they were driving on the freeway that night.

Bundgaard had told the police earlier that as they were driving, she opened the car’s door and the interior light came on, and that’s when he reached across her chest and grabbed her.

He had maintained he never intentionally tried to harm her.

Meanwhile, the Senate’s attorneys are calling a few more witnesses, including two law professors, who will back their suggestion that the committee should recommend Bundgaard’s expulsion. The committee could also issue a formal censure or dismiss the complaint outright.

Attorney Kory Langhofer, the Senate’s investigator, also called a polygraph expert to persuade the panel that a lie-detector test that Bundgaard took after the February scuffle was “unreliable.”