With three prominent Democratic senators now on record raising the issue of John McCain's health, and an independent group set to make a push for the full release of the Arizonan's medical records later this week, the issue of the Republican nominee's age is being dragged further out into the political spotlight.

Speaking to ABC's George Stephanopolous on Sunday, Sen. Claire McCaskill refused to back away from her statement, earlier in the week, that Alaska Gov. Sarah Palin wants to serve one heartbeat away from "one of the oldest presidents" in history. Given the opportunity to walk back the remarks -- which McCain aides derided as ageism -- McCaskill did the opposite, saying: "I think what we're talking about is a reality. Other people talk about his melanoma. We're talking about a reality here that we have to face."

In the Senate Democratic cloakroom, at least, she's not alone. During the Democratic convention, OpenLeft's Matt Stoller asked Senate Majority Leader Harry Reid and senior New York Senator Charles Schumer about McCain's cancer history. Both replied that a full release of McCain's medical records would be an appropriate way to satisfy the public's right to know.

"We learned that going back a long time ago...when Tom Eagleton, because of his depression, had had shock treatment. So this isn't something we just dreamed up, it's important," Reid said, adding, "I think there should be total transparency when a person is running for President of the United States." Schumer took a similar line: "When you're running for President everything should be public including your full medical records."

Somewhat predictably, fellow Arizona Sen. John Kyl was taped saying he takes McCain at his word when his colleague says his cancer is in remission.

But on Thursday, the progressive group Brave New Films is prepared to list the names of 2,000 doctors who say McCain's word is not sufficient on this score, and that he should release his entire medical records to the public. Previously, McCain made his medical records available to select members of the press for only a few hours -- a time span during which electronic devices were prohibited and copies could not be made.

(You can read the text of the Brave New Films letter signed by doctors, and watch an accompanying video, here.)

While McCain's choice of a relative unknown like Sarah Palin has been praised as genius politics in some circles, it appears her selection may have also opened the door to more direct implications about the senator's age and health. Whether or not that increased attention sways any voters, however, remains to be seen.