“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 TesterJonathan (Jon) TesterOvernight Cybersecurity: Equifax security employee left after breach | Lawmakers float bill to reform warrantless surveillance | Intel leaders keeping collusion probe open Overnight Finance: White House requests B for disaster relief | Ex-Equifax chief grilled over stock sales | House panel approves B for border wall | Tax plan puts swing-state Republicans in tough spot Senators grill ex-Equifax CEO over stock sales 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.