“The stakes are high, Montana,” Romney said in the ad, which started running statewide this week. “I urge you to send Denny to the Senate, and we’ll get America back on track.”

Rehberg is in a tight election against incumbent Sen. Jon TesterJon TesterDem senator to appear with Romney: report Battle begins over Wall Street rules Dems hunt for a win in Montana special election MORE (D-Mont.).

In the ad, Romney also points to high unemployment and the rising national debt, adding, “We’ve lost thousands of jobs, yet Senate Democrats want higher taxes, more spending.”

Tester hasn’t used President Obama in any of his own ads, though Rehberg has tried to tie him to Obama. Tester has been playing up his independent record and bipartisan legislative work.