The plan’s odds just improved dramatically.

Sen. John McCain (R-AZ) said Thursday morning that he would support his party’s tax overhaul, a huge win for Republican leaders that could help pave the way for the upper chamber to pass its bill in the next 24 hours.

“After careful thought and consideration, I have decided to support the Senate tax reform bill,” McCain said. “I believe this legislation, though far from perfect, would enhance American competitiveness, boost the economy, and provide long-overdue tax relief for middle-class families.”

The Arizona senator was one of the votes most in doubt. Whip counts shared by lobbyists in recent weeks counted him as a “no” vote. Senate Republicans need 50 of their 52 members to back the tax bill, so every vote counts. McCain had already shown during the Obamacare repeal debate that he was willing to vote down his party’s top legislative priority.

Under the Senate bill, the corporate tax rate would be slashed from 35 percent to 20 percent, and the individual tax code would be overhauled in a way that sends most of the benefits to the wealthiest Americans. McCain voted against the Bush tax cuts back in 2001 and 2003 because they disproportionately benefited the most well-off.

The bill is also undergoing significant last-minute changes, which could redirect hundreds of billions of dollars in the US economy over the next decade. Yet McCain, who has been obsessed with regular order and voted against the final Obamacare repeal bill because it was slapped together at the last minute, seems satisfied with the process that produced the Senate tax plan.

“For months, I have called for a return to regular order, and I am pleased that this important bill was considered through the normal legislative processes, with several hearings and a thorough markup in the Senate Read More Here