Maria Cantwell intends to vote for the bill, her spokesman tells me. She was won over by a letter from Commodity Futures Trading Commission Chairman Gary Gensler, in which he reassured her the language regulating derivatives is sufficiently clear and enforceable. Cantwell voted against the original Senate version because of concerns that there were loopholes in that portion of the legislation.

Her vote means Democrats will only need to win over two of the four fence-sitting Republicans to clear procedural hurdles in the Senate. Susan Collins has already suggested she’s inclined to support the bill, leaving Olympia Snowe, Chuck Grassley and Scott Brown as three potential pick-ups to put the legislation over the top.

Jay reported earlier today that “Harry Reid’s staff didn’t seem too worried” about getting the votes. Cantwell’s support gives them that much more breathing room headed into the recess.

Cantwell’s statement and Gensler’s full letter after the jump: