Presidents of the United States usually manage to cultivate friendships in the least-expected places.

Democrat Lyndon Johnson had strong alliances with Republican Sen. Everett Dirksen; Republican Ronald Reagan had a marvelous after-hours social friendship with Democratic House Speaker Thomas “Tip” O’Neill; Democrat Bill Clinton worked with Republican Speaker Newt Gingrich to produce a balanced federal budget; Republican George W. Bush and Democratic Sen. Ted Kennedy worked hand-in-glove to craft education reform legislation.

They all sought each other out in the search for common ground. It worked. The government found a way to get things done. The outreach extends in both directions.

That’s how good government works.

Donald Trump’s approach? Bash ’em all. Democrats and Republicans alike all feel the sting of Trump’s Twitter tirade. Criticize the president on policy differences? You’d better don your hard hat to avoid getting your bell rung by rhetorical abuse delivered — of course! — via Twitter.

Trump is at it again. He calls for “national unity.” Then unleashes yet another Twitter broadside.

The president is an angry man. His anger is threatening to stall everything in Congress. He has impugned the very people he needs: Senate Majority Leader Mitch McConnell, Speaker Paul Ryan, Senate Armed Services Committee Chairman John McCain … and on and on it goes.

Everyone has his or her limits to their level of anger. How far is Donald Trump going to take his myriad feuds with members of both parties in Congress?

I’m going to presume we’ll know when it occurs when Trump’s anger hits the proverbial wall.