Sen. Rand Paul (R-Ky.), who has libertarian leanings, has often found himself at odds with some of the actions of his own party. Republican Sens. Lisa Murkowski (Alaska), and Susan Collins (Maine), are considered the left fringe of the Republican Party and also frequently oppose its initiatives.
Sen. Tom Tillis, R-N.C., differs on whether the president can bypass congressional spending limits and fund wall construction with his emergency declaration, but otherwise has been with the administration on nearly all significant votes.
But the fact those four have announced they plan to vote against the president on a resolution that would overturn his national emergency declaration – a vote they can take comfort in the notion Trump will veto it and neither house of Congress has the votes to override the veto – was presented Tuesday by both the Washington Post and New York Times as evidence the president’s stranglehold on support among Republicans is starting to break.’
“Trump’s Grip Shows Signs of Slipping as Senate Prepares to Block Wall Emergency,” read the headline on a piece by Sheryl Gay Stolberg and Emily Cochrane in the New York Times.  “Cracks show in wall of Republican support for Trump,” read the headline the same day on Jacqueline Alemany’s story in the Washington Post. 
The politicians involved have been careful to point this does not indicate a larger break with Trump but rather was specific to this issue.
“’It simply sends a message that Congress is going to stand up for its institutional prerogatives and abide by the separation-of-powers framework that was carefully worked out by the framers in the Constitution,” the Times quoted Collins as saying.  “’I truly don’t see this as sending a message at all one way or the other about border security but rather about executive overreach.’”
“It’s not like I sat up one day and said, ‘Where do I want to separate myself from President Trump?’” he wrote . “There are political risks to separating yourself from your own party’s president. To me, it isn’t even about immigration, it isn’t about Republican or Democratic president. It’s about Congress versus the president and where the power should be distributed.”
Despite both senators’ insistence this was not about stopping the wall from being built, Alemany wrote : “Senate Republicans seem to have the numbers to defy Trump on his signature campaign issue – building the wall,” even though “the political imperative to stick with the president – a defining feature of congressional Republicans under Trump – remains.”
Two paragraphs later, though, she quotes an anonymous aide to a Senate Republican saying, “My boss is worried about arguments made about Democrats coming back to use the emergency declaration. But … they’ll stand with the president because all hell breaks out when you oppose him – especially in red states.”
To make its point about support eroding for the president, the Times quotes Ross Baker , a political scientist at Rutgers, who said passage of the resolution would be “’a serious rebuke’ of the president” and an indication “This has gone far enough’” – further implying there are other underlying factors separating the president from his allies in Congress.
It then outlines the history of confrontations  between presidents and Congress over the limits on executive power, saying it dated to at least the time of Richard Nixon.
“Democrats fumed at what they viewed as President George W. Bush’s expansive use of his executive powers; Republicans routinely accused President Barack Obama of exceeding his authority on issues like combating climate change and protecting certain classes of undocumented immigrants.
“But Mr. Trump’s declaration of a national emergency to fulfill a campaign promise to build the wall – issued after Congress denied him the money for it – strikes many lawmakers as a direct incursion on a power granted exclusively to Congress in the Constitution: the power of the purse.”
Congress did not deny Trump money for the wall. It gave him $1.375 billion toward wall construction.