Last-minute threats to the tax cuts that Trump has promised since early in his long-shot presidential campaign are looming among Senate Republicans. Concerns center on the taxation of partnerships, limited liabilities and other companies; on the overall cost of the tax bill itself; and on a familiar GOP stumbling block -- Obamacare.

"It's not going to be easy," Senate Finance Committee Chairman Orrin Hatch of Utah said Monday. "This is going to be a tough, tough time."

Senate Republican leaders aren't counting on any Democrats for a floor vote that could come Thursday or Friday -- but that means they can afford to lose only two members of their own party. Here are the eight GOP senators most likely to decide the tax bill's fate.

Corker, the retiring Tennessee Republican has staked a hard line against letting tax legislation add to federal deficits -- saying that a single penny of new deficits would lose his vote. It turns out the Senate bill would add $1.4 trillion to the deficit over 10 years -- at least before accounting for any economic growth -- according to a Congressional Budget Office reportreleased Sunday.