Sen. Fred Thompson (R-Tenn.), who was among those seeking the Republican presidential nomination this year, cut a radio ad for California GOP candidate Tom McClintockThomas (Tom) Milller McClintockAn attack on America that's divided Congress — and a nation Coalition of 7 conservative House Republicans says they won't challenge election results Five Republicans vote for bill to decriminalize marijuana MORE, who is running in California's 4th Congressional District to replace the retiring Rep. John Doolittle (R).

McClintock is a nationally recognized budget expert, Thompson says in the one-minute ad, while McClintock's Democratic opponent, Air Force veteran Charlie Brown, is an "amateur," Thompson implies.

"Democrats, Republicans, and Independents all agree when it comes to watching the budget and fighting for the taxpayer, Tom McClintock is the one we can trust," the former Law & Order star says. (Listen to the ad here.)

McClintock has been locked in a close battle with Brown to retain control of the seat for Republicans after Doolittle has been dogged by allegations of an improper relationship with disgraced lobbyist Jack Abramoff.

A poll released by McClintock's campaign earlier this week showed him leading with 47 percent in the race, besting Brown, who drew 39 percent.

-Michael O'Brien