Democrat John Walsh hasn't been in the U.S. Senate for even a week, but already a battle to define him over the airwaves is well underway in Montana.

The ads focus on Walsh's military record. The latest offering came Friday when Walsh's campaign released an extended commercial defending his record and pushing back against GOP attacks. The ad features a veteran who served with Walsh in Iraq and was shot by a sniper.

"General Walsh fought them for what we, as soldiers, needed," says the veteran, retired staff sergeant John Bennett.

Walsh appears later in the spot, saying, "I understand what courage really is. I led Montana's finest men and women into combat in Iraq. And I carry with me the names of four soldiers I had the honor to serve with who didn't make it home. So it's going to take a lot more than smear ads to deter me from taking on Washington."

The ad is a longer version of a spot the campaign released earlier this week. The ads are meant to respond to a commercial from the GOP group American Crossroads that slams Walsh over an Army Inspector General's report that said Walsh improperly solicited other National Guard leaders to join an association in which he was running for vice chairman. Walsh is a former adjutant general of the Montana National Guard.

"Walsh was formally reprimanded by the U.S. Army," says the narrator of the Crossroads ad.

Walsh's ad says he was reprimanded for "defending Montana’s troops."

Gov. Steve Bullock (D) appointed Walsh -- then his lieutenant governor -- to the Senate last week to replace Democrat Max Baucus, the new ambassador to China. Walsh was already running for the seat which Baucus planned to vacate anyway.

Bullock's appointment was seen as a boon to Democrats' hopes of keeping the Senate seat. Walsh will now have the benefits of incumbency: Greater visibility and name recognition, better access to donors by virtue of his new power, and a chance to establish a voting record.

He'll need all the help he can get against top GOP recruit Rep. Steve Daines (R) in the conservative-leaning state.