Dan Sullivan and Lisa Murkowski of Alaska
Jeff Flake and John McCain of Arizona
Cory Gardner of Colorado
Marco Rubio of Florida
Rand Paul of Kentucky
Susan Collins of Maine
Ben Sasse of Nebraska
Dean Heller of Nevada
Rob Portman of Ohio
Pat Toomey of Pennsylvania
Lindsey Graham of South Carolina
Lamar Alexander of Tennessee
Mike Lee of Utah
Shelley Moore Capito of West Virginia
We must realize that Donald Trump is not really a Republican or a conservative, and is impossible to figure out what his agenda is, so that means that there will be a “firewall” of Republicans in the US Senate, who at least in some cases, can be added to Democratic opposition in the Senate, and give some hope that there will be control over Trump appointments and initiatives over the next few years.
Not all of the above list will cooperate and collaborate together on all issues, but they all seem to be likely to fight Trump on some issues, and if three or four work together with a united Democratic Party in the Senate, Trump will be unable to accomplish all his goals, and he is likely to bitterly denounce these Republicans, and cause, by his language, more stalemate and gridlock, and prevent the most grievous nominees and parts of his agenda.
The most likely to oppose Trump are the following: Susan Collins, Lisa Murkowski, John McCain, Lindsey Graham, Rand Paul, Marco Rubio, Jeff Flake, and Rob Portman in that order.
However, Ben Sasse and Mike Lee, as strong conservatives, are also likely to try to limit Trump Administration goals if they find them objectionable.
The others–Dan Sullivan, Cory Gardner, Dean Heller, Pat Toomey, Lamar Alexander, and Shelley Moore Capito–may, occasionally, join with the members of this group.
Remember that seven of this group—Murkowski, McCain, Rubio, Paul, Portman, Toomey, and Lee have a new six year term, so are not threatened by Trump as far as their Senate seat is concerned.
Only Flake and Heller face election contests in 2018, while the other seven –Sullivan, Gardner, Collins, Sasse, Graham, Alexander, and Capito face election in 2020.
So 16 Senators out of 52 Republicans, fully one third, could stand in the way of Donald Trump, and if he went too far in abuse of his powers, could, potentially, join in a possible move to promote impeachment, although even if all 48 Democrats joined in, would still fall short of the 67 needed to convict and remove him by three votes.