Brian Beutler June 28, 2010, 9:50 AM

Today the Senate will mourn the passing of its longest serving member in history, Robert Byrd (D-WV). But by week’s end, Democrats want to pass final — and unamendable — legislation, rewriting the rules that govern Wall Street. And they have no margin for error — or for losing a colleague.

The Senate’s financial reform bill passed in May with four Republican votes: Sens. Chuck Grassley (R-IA), Olympia Snowe (R-ME), Susan Collins (R-ME), and Scott Brown (R-MA). Snowe and Collins are thought to be reliable supporters of the legislation. Grassley’s a question mark: He actually supported a filibuster of the Senate bill, before switching and voting for final passage. Brown was always thought to be the linchpin. Congressional Democrats and the White House have wooed him for weeks, and protected at least one big loophole on his behalf, in order to retain his support.

Then, late last week, Brown changed his mind. Or at least he threatened to — over opposition to a fee on banks, added to the legislation late in the game.

Republicans will likely hold the conference report to a 60 vote threshold. If Brown bolts now, then, Democrats will have to do one of four things:

1. Wait until West Virginia Gov. Joe Manchin appoints a replacement, and hope that Grassley doesn’t waver, which would perhaps push them past their self-imposed deadline to finish the bill this week.
2. Persuade Sen. Russ Feingold (D-WI), Maria Cantwell (D-WA), or both to switch their votes from “no” to yes” (they opposed the bill from the left).
3. An unlikely choice: reconvene the conference committee to remove the bank fees Brown opposes, also threatening the end-of-the-week .
4. An unlikelier choice: Let Republicans vote it down.

That last option probably means the bill dies, though Democrats could demagogue its potential demise to try and force one or two Republicans to break with their party.

We should know more by day’s end how Democrats (and Republicans) plan to proceed, and how Byrd’s death actually changes the math on this bill. And it could be that Brown will still support the bill, despite his ominous statement But this is yet another reminder of how slim the Democrats’ seemingly large majority actually is when Republicans invoke filibuster rules, and then band together in opposition.

Chuck Grassley, Filibuster, Financial Reform, Maria Cantwell, Olympia Snowe, Republicans, Robert Byrd, Russ Feingold, Scott Brown, Senate, Senate Republicans, Susan Collins, Wall Street, White House