“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 TesterWhy 'cherry-picking' is the solution to our nation’s flood insurance disaster Trump signs Veterans Affairs bill at New Jersey golf club It's time for McConnell to fight with Trump instead of against him 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.