As lawmakers in Congress from both parties anxiously await the fine print of a major tax reform plan from Republicans, President Trump's Sunday social media spat with a key GOP Senator was a reminder that the White House may be in a more precarious political situation when it comes to getting the votes for tax reform, than the recently failed effort on changes to the Obama health law.
"Count me out if it adds a penny to the deficit," Sen. Bob Corker (R-TN) said last week about the outlines of a GOP tax reform bill, as the Tennessee Republican has made clear he will vote to start the tax reform process - but not necessarily back the final product.
"I think the deficit is the greatest threat to our nation," Corker said just off the Senate floor, arguing that Republicans in Congress and the White House seem to have forgotten their vow to restrain spending.
"I feel like in some ways - since Election Day - we've moved into a party atmosphere here, and that concerns me," Corker added.
Those words - and other criticisms - made the President boil over on Sunday, when he sent out a string of highly critical tweets aimed at the Senator.
"I would fully expect Corker to be a negative voice and stand in the way of our great agenda," Mr. Trump tweeted.
While those tweets might make the President and his allies feel good, Republicans simply can't lose votes like Corker - especially in the Senate, where like on health care, if three GOP Senators go against Mr. Trump, tax reform legislation won't be approved.
Along with Corker's shot across the bow on the deficit, Sen. Rand Paul (R-KY) has repeatedly made clear that he doesn't like the details made public so far on tax reform, saying the GOP plan looks like it will end up raising taxes on many middle class voters.
"We must speak up and fix this plan," Paul wrote in an op-ed piece for Forbes Magazine.
"What I will not accept is a tax hike on the middle and upper middle class, sacrificing their paychecks on the altar of “reform," Paul wrote.
Those type of red flags - before the details are even out - have some Republicans concerned.
"I wish we had 62 Republicans instead of 52," said Sen. John Kennedy (R-LA). "But we don't."
Even before we know all the details of the tax reform plan, one item is getting a lot of attention, and that is the stated goal of the White House and GOP leaders in Congress to end the deduction for state and local taxes.
"To lose deductibility of state and local taxes is unfair, and I'm going to continue to fight it," said Rep. Tom MacArthur (R-NJ).
"I am going to do what I can to rally states like New Jersey, New York, Pennsylvania, California, Illinois, Connecticut," MacArthur told reporters off the House floor. "It's not fair to give the entire country a tax break on the back of the citizens of these six or seven states."
It's not just more moderate Republicans from East Coast states with higher taxes who have raised questions about the possibility of doing away with the state and local tax deduction.
"It is not" just Blue States, said Rep. Kenny Marchant (R-TX), who says that local property taxes in Texas can certainly be a big write-off for itemizers in the Lone Star State as well.
"I'm from a high property tax state," Marchant told reporters, acknowledging that a number of GOP colleagues have made it clear to the tax writing Ways and Means Committee that they don't want the state and local tax deduction phased out.
"There are some people who say, it isn't a big issue back home," said Rep. Mike Kelly (R-PA). "Well, in some places, it is the issue back home.
The state and local tax deduction isn't the only possible pitfall for Republicans - more will likely emerge once the tax-writing committees in the House and Senate produce an actual draft tax reform bill, chock full of all sorts of details.
The goal is to do that in October - but it could still slip.
And if you are going to do a full tax reform bill, there will be a never-ending source of stories about whatever is in those details.
"Tax Reform is needed more than ever before. Go Congress, go!" the President tweeted last month.
But if Mr. Trump battles more with individual GOP lawmakers in the Congress, it could make that drive for tax reform even more difficult.