While Blunt's growing opposition to the legislation is expected, McCaskill's moves are more significant because of fragile vote margin Senate Democrats hold in the upper chamber.
Missouri's junior Senator joined a group of eight moderate Democrats who want leadership to post the health care legislation and budget office projections on the Internet for 72 hours before votes are cast.
"Every step of the process needs to be transparent, and information regarding the bill needs to be readily available to our constituents before the Senate starts to vote on legislation that will affect the lives of every American," wrote McCaskill in a letter, joining seven other Democrats.
The move for greater transparency has the ranking Republican on the Senate Finance Committee speculating that McCaskill -- along with the others -- could possibly end up as potential 'no' votes as the debate unfolds.
"There's -- there's just some nervousness, I guess I would call it -- not any more so than in the Republican Party -- about some of the things that might be in the bill," Sen. Chuck Grassley said, according to The Hill.
"Moderate Democrats and Republicans have reason to be worried," wrote The Wall Street Journal's John Fund about the concerns.
The right's wishful thinking may be overblown. McCaskill stood in raucous town hall meetings this summer defending the public option and the need for expanded coverage. But she's politically savvy enough to know that this vote could define President Obama's re-election prospects in 2012, when she'll be running -- whether she likes it or not -- as a candidate closely aligned with his agenda.
With one eye on the upper chamber in 2010, Blunt joined a group of House Republicans Wednesday to highlight more than $500 billion dollars in cuts to the Medicare program.
While Democrats scoffed at Blunt's defense of Medicare just weeks after he was caught on tape saying the program has "never done anything to make people more healthy," Blunt called the belief that cutting funding wouldn't result in negative consequences, "the biggest fallacy in this new plan."
He added that the effect would be "to put Medicare in jeopardy."
The CBO estimated that Sen. Max Baucus' bill would cost $829 billion dollars over a 10-year period and cover 94 percent of eligible Americans. Baucus seemed to indicate that this legislation would likely make it to the floor for a vote.
If leadership does not accept McCaskill's transparency requests, her next choice will become even more difficult.
For Blunt, the choice was made a long time ago.
Columnist David Broder notes that while prominent Republicans from former Majority Leader Bill Frist to former Health and Human Services Secretary Tommy Thompson have urged the GOP to get on board in some fashion, Blunt isn't likely to budge.
"There has been no real pressure from business" to move the legislation forward, Blunt told Broder, adding that there's "growing skepticism about what business can expect from any reforms."
"The House and Senate (Democratic) leaders say they are not bound by any agreements the White House has made," Blunt noted.