Liberal groups on air blasting Heller, Berg for voting to 'end Medicare as we know it'

Heller and Berg are both in competitive Senate races where the outcomes could determine control of the upper chamber in the next Congress. 

Majority PAC is the group behind the ad against Berg. 

"To get ahead in Washington, Rick Berg voted the party line to end Medicare as we know it, change Medicare to a voucher system run by big insurance companies that cuts prescription drug coverage and doubles out-of-pocket expenses for seniors, all while Rick voted down the line to protect tax breaks for millionaires like himself and giant corporations," the ad says. "Rick Berg has changed. He's already another Washington politician."

Patriot Majority is the group behind the anti-Heller ad, its third of the campaign. It rips Heller for voting "to end Medicare not once, but twice, once as a congressman and again as a senator," and calls the plan "disastrous" and "insanity."

The ads against Heller have $200,000 a week behind them, a hefty buy. Majority PAC told The Hill their buy was in the low six figures.

Berg is locked in a tight race against former North Dakota Attorney General Heidi Heitkamp (D) despite the state's strong Republican leanings, while Heller is in what has been a nip-and-tuck race against Rep. Shelley Berkley (D-Nev.).

The House Ethics Committee on Monday, however, announced it would investigate whether Berkley violated House rules by using her position in Congress to benefit her husband’s medical practice, a move that could prove very damaging to her campaign. The Hill rates both races as "toss-ups" for now.

This post was updated at 12:45 p.m.