I wonder if "Mainstreet Partnership lawmakers" is the same as "Republican Main Street Partnership committee"? The later name is from the Bloomberg article.
The Washington Times reports on how the vote on the Medicare Bill is already a political factor:
The Republican Main Street Partnership began running a radio ad Wednesday against Rep. Patrick J. Toomey, Pennsylvania Republican, for voting with 24 other conservatives against the $395 billion bill President Bush is set to sign Monday. Mr. Toomey, who said the bill didn't adequately reform Medicare and was too costly, is running in the Republican primary for the Senate seat of Sen. Arlen Specter, whom the partnership backs.
"Pat Toomey slammed the door on President Bush, who championed the Medicare bill," says the ad, which airs on a Harrisburg station through Dec. 16.
Specter's definitely benefitting from these people.