Sen. John McCain offered sharp criticism of President Donald Trump in a op-ed Friday in which he called for Congress to return to its regular order.

Writing in The Washington Post, the Arizona Republican argued that Congress should seek policy compromise following a GOP Obamacare repeal process that he repeatedly slammed. McCain, a frequent critic of Trump, said bipartisanship in Congress is particularly important because Trump is president.

"But we have to respect each other or at least respect the fact that we need each other," McCain wrote. "That has never been truer than today, when Congress must govern with a president who has no experience of public office, is often poorly informed and can be impulsive in his speech and conduct."

"We must respect his authority and constitutional responsibilities. We must, where we can, cooperate with him. But we are not his subordinates. We don't answer to him. We answer to the American people. We must be diligent in discharging our responsibility to serve as a check on his power. And we should value our identity as members of Congress more than our partisan affiliation," the senator added.

McCain, 81, was one of three Republican senators who voted against a last-ditch GOP attempt to repeal Obamacare in July, shortly after he was diagnosed with brain cancer. He argued against the hurried Republican-led process to overhaul the U.S. health-care system that moved forward without relevant committee hearings.

Since taking office in January, Trump has sometimes spoken of Republican members of Congress as if they serve him and owe him loyalty.

He has also apparently improvised some consequential comments, like his threat to bring "fire and fury" on North Korea.

Read the full McCain op-ed here.