Tax reform is moving forward in Washington but significant hurdles remain and a government shutdown could still happen.

Senate Republicans advanced their tax bill on Tuesday after the budget committee passed it on a party-line vote. Now the task is getting it through the full Senate.

Senate Majority Leader Mitch McConnell, R-Ky., said, “It’s a challenging exercise. Think of sitting there with a Rubik’s cube trying to get to 50.”

Republicans need at least 50 votes to pass the bill and they control the Senate with just 52 senators. That means they can only afford two defectors and right now half a dozen or more are up in the air.

One concern is a mechanism to automatically trigger tax increases if annual economic growth goals aren’t met.

The New York Times reports that Sen. John McCain could sink the whole deal as he did with the move to repeal Obamacare. McCain has praised parts of the bill but could still vote no.

The president spent Tuesday pushing reform on Capitol Hill. He was supposed to meet with the Democratic Senate and House leaders but it all fell apart. Trump tweeted, “I don’t see a deal” and then Senate Minority leader Chuck Schumer and House Minority leader Nancy Pelosi backed out of their meeting.

Schumer complained, “The President said ‘I don’t see a deal’ three hours before our meeting, before he heard anything we had to say.”

Flanked by empty chairs representing Schumer and Pelosi the president went ahead and met with Republican leaders Mitch McConnell and Paul Ryan.

“They decided not to show up. They’ve been all talk and no action,” said Trump.

If no action continues into next week it could spell trouble. A temporary spending bill expires Dec. 8th and a new one is needed to prevent a government shutdown.