Michael J. Fox is making his return to the midterm elections.

After cutting some memorable campaign commercials for now-Sens. Ben CardinBen CardinWarren wants briefing on probe into Trump ally A guide to the committees: Senate House bill would prevent Trump from lifting Russian sanctions MORE (D-Md.) and Claire McCaskillClaire McCaskillA guide to the committees: Senate Juan Williams: Senate GOP begins to push Trump away Dem senator: I may face 2018 primary from Tea Party-esque progressives MORE (D-Mo.) four years ago, Fox is back in a new spot for Sen. Arlen Specter (D-Pa.).

"Arlen Specter is moving forward," Fox says. "He's won the battles to double funding for biomedical research, to find cures and to save lives.

"He's smart, tough and always moving forward."

Fox's 2006 midterm ads for Cardin and McCaskill drew plenty of attention, especially after Rush Limbaugh accused him of exaggerating the effects of his Parkinson's disease during the ads.

Specter faces Rep. Joe Sestak (D-Pa.) in the May 18 primary. If he wins there, polls show he would also face a tough match in November, with former Rep. Pat Toomey (R-Pa.) leading.