Sen. Bob Corker (R-Tenn.) has expressed concern with the GOP tax bill's impact on the deficit. (Joshua Roberts/Reuters)

Sen. Bob Corker (R-Tenn.) says he'll vote against Senate Republicans' tax plan, saying the $1 trillion it's projected to add to the deficit is too much for him to swallow. But his vote probably won't matter: Even without Corker, Republicans appear to have the votes they need to pass the bill anyway.

Corker's real chance to block the tax plan may have passed him by three days ago.

On Tuesday, Corker voted the tax bill out of the Senate Budget Committee, sending it to the Senate floor by an 12 to 11 margin — meaning had he joined with Democrats, the committee would have voted against it.

That would not have killed the bill. Senate Majority Leader Mitch McConnell (R-Ky.) could have sent it to the Senate floor without the committee's approval, and on a vote where only three Republicans' defections would sink the measure, that departure from the Senate's “regular order” would have jeopardized the effort. It was “regular order,” after all, that made the list of grievances Sen. John McCain (R-Ariz.) cited this summer in his late-night vote to stop the GOP from repealing large chunks of the Affordable Care Act.

So why did Corker pass on the chance?

At the time, Corker said he believed Senate leaders were committed to adding a “trigger” to the bill, which would force automatic tax increases if projections of economic growth fell short. “After agreeing in principle with Senate leadership, members of the finance committee, and the administration on a trigger mechanism to ensure greater fiscal responsibility should economic growth estimates not be realized, I voted today to advance this important piece of legislation,” Corker said in a statement after voting the bill out of the Senate Budget Committee. “While we are still working to finalize the details, I am encouraged by our discussions.”

But after the bill cleared the budget committee, the Senate parliamentarian ruled the “trigger” idea was not in keeping with the special Senate procedures the GOP is trying to use to pass the measure with just 50 votes, and the idea was dropped.

Corker had hoped to find another way to add more tax revenue back into the bill and shrink its deficit gap, but conservatives balked at that plan. And on Friday morning, Corker's top ally in the deficit hawk coalition — Sen. Jeff Flake (R-Ariz.) — said he'd support the measure, leaving Corker alone.

Corker's opposition hardened following a report Thursday night from Congress's official tax scorekeeper that concluded the bill would add $1 trillion to the deficit over a decade.

He has been adamant for months that the Republican bill not balloon the federal debt. “I came here because of fiscal concerns. I’ve seen no real movement, matter of fact probably negative movement, as it relates to deficit issues,” Corker said earlier this week in the face of intense intraparty pressure to support the tax bill. “And what I don’t want to do is be a part of something where I’m knowingly involved in making that situation worse.”

But with Sens. Susan Collins (R-Maine), Ron Johnson (R-Wis.) and Flake now supporting the bill, McConnell is expressing confidence it will pass on Friday night.

“This is yet another tough vote. I am disappointed. I wanted to get to yes,” Corker said in announcing his plan to oppose the bill on the Senate floor. “But at the end of the day, I am not able to cast aside my fiscal concerns and vote for legislation that I believe, based on the information I currently have, could deepen the debt burden on future generations.”

The Senate is on schedule to cast a final vote on the bill. This time, it appears there's nothing Corker can do to stop it.