In a television commercial, two liberal political action committees - Brave New PAC and Democracy for America – have launched an aggressive attack on John McCain’s past bouts with skin cancer. The 30-second ad features unflattering images of McCain’s melanoma scars, calling for the Republican presidential nominee to release his medical records to the public. The ad is the most public and unflinching effort to turn McCain’s health into a political issue.

The ad, so far airing for a $50,000 buy over a few days on MSNBC, is paid for by a political group headed by James Dean, the brother of Democratic National Committee Chairman Howard Dean. The makers of the ad hope to extend the buy to battleground states or possibly purchase a full page ad in the NY Times in the coming weeks if they are able to raise necessary funds through donations from supporters.

In the ad, two doctors express concern about McCain’s ability to deal with a new cancer episode. Dr. Michael D. Fratkin says: “Another bout of cancer for John McCain while he is president of the United States would profoundly impact his capacity lead.” Dr. Noah Craft explains it thus: “Melanoma is the deadliest of skin cancers. The chances of survival if you have melanoma spread through your body are very slim.”

The graphic text at the end of the ad, over a black-and-white image of McCain with the left side of his face bandaged after surgery in 2000, says: “John McCain is 72 years old and had cancer 4 times. Why won’t McCain release his medical records?”

Brave New PAC spokesman, Axel Woolfolk, told CBS News that in addition to the ad, the groups have also initiated a petition for doctors with the hope that with enough signatures they will “ultimately deliver the petition and create enough grassroots support to get a full disclosure of the [medical] records. So far, about 2,500 doctors are reported to have signed the petition.

Expressing his reaction over the ad, RNC spokesman Danny Diaz said: “The fact that Howard Dean’s brother and an adviser to the Obama campaign are behind despicable and cheap smear ads against Senator McCain is deeply disappointing, but in no way surprising. Barack Obama has promised Americans an elevated debate offering nothing but gutter, Chicago-style politics.”