Republicans Turn on Bush:

"Concerned about an expected budget deficit of $477 billion this year, four members of Bush's own party voted in favor of an amendment that offers two ways of paying for tax cuts -- find funds in the budget to pay for them, or obtain 60 votes in favor in the 100-member Senate.

Republicans now control 51 seats in the Senate, so they would need to persuade some Democrats to vote with them to obtain the 60-vote mark. Most routine measures require only a simple majority to pass in the Senate. "