Well there are several Republican parties. I gather you’re talking about the one infested by John Cornyn, Marco Rubio, Mitch McConnell, John McCain, Mitt Romney, John Boehner and that lot, right?
The author confuses “Republican Party” with “conservatives.” There is a very small conservative contingent in Washington, D.C. This doesn’t change even if the Republican Party controls the White House and both Houses of Congress.