WASHINGTON — Senate Republicans, increasingly unnerved by President Donald Trump’s volatility and unpopularity, are starting to show signs of breaking away from him as they try to forge a more traditional Republican agenda and protect their political fortunes.

Several Republicans have openly questioned Trump’s decision to fire FBI Director James Comey and even lawmakers who supported the move have complained privately that it was poorly timed and disruptive to their work. Many were dismayed when Trump seemed to then threaten Comey not to leak negative information about him.

As they pursue their own agenda, Republican senators are drafting a health care bill with little White House input, seeking to avoid the public relations pitfalls that befell the House as it passed its own deeply unpopular version. Republicans are also pushing back on the president’s impending budget request — including, notably, a provision that would nearly eliminate funding for the national drug control office amid an opioid epidemic. And many high-ranking Republicans have said they will not support any move by Trump to withdraw from the North American Free Trade Agreement.