Many of us have, on one or more occasions, harmed ourselves with a tweet. But most of us are not the president.

President Trump too often uses Twitter to stream his thoughts directly to the world. Some of his supporters revel in the howls these tweets produce from news media and other critics. This trollish appreciation misses the main consequence, that Trump imperils his own agenda, much of which we agree with, when he tweets from the hip.

"[T]weets on legal matters seriously undermine Admin agenda and POTUS," wrote respected Republican attorney George Conway, husband of Kellyanne Conway, councilor to the president. He continued, "and those who support him, as I do, need to reinforce that and not be shy about it."

Conway is right, and early on the morning after the London Bridge terrorist attack, in a span of 14 minutes, Trump rattled off a series of tweets that demonstrated his potential and actual self-harm.

"We need to be smart, vigilant and tough," he wrote to start the tweetstorm. "We need the courts to give us back our rights. We need the Travel Ban as an extra level of safety!"

Trump's own White House had repeatedly rejected the label "travel ban" and said the president's executive order was instead a system for vetting visitors. This is mostly a rhetorical point, but it has some legal bearing.

Federal law grants the president power to "suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants ... for such period as he shall deem necessary."

A temporary suspension may be regarded by judges as different from a ban, and so calling it a ban might undermine the legal defense of the order. But on the legal front, Trump's follow-up tweets could be even more harmful.

Perhaps bugged when MSNBC's Morning Joe contrasted Trump's tweets about the "ban" with Spicer's comments, Trump tweeted again Monday morning, calling the "ban" a "watered-down" version of the original order, which had been struck down more unequivocally by the courts. The government has argued in court that the more recent order was a different thing from the original, not merely a new version of it. Trump undermines that argument with his tweets, thus hurting his own legal case.

"In general," conservative legal scholar Joshua Blackman wrote on Monday, "talkative clients pose distinct difficulties for attorneys, as statements outside the court can frustrate strategies inside the court. These difficulties are amplified exponentially when the client is the president of the United States…"

But Trump had yet more to say.

"Do you notice we are not having a gun debate right now?" Trump wrote amid his Sunday morning tweetstorm. "That's because they used knives and a truck!"

Maybe Trump thought he was pointing out an inconsistency in media coverage of terrorist attacks. Instead, he was unwittingly making an argument for gun control. We believe in gun rights, but in this case it seems clear that the terrorists would have killed more people had they been armed with guns, as the Paris terrorist were in November 2015.

Trump is highlighting a point that cuts against his stated belief in gun rights.

Finally, Trump also for good measure tweeted his scorn for the mayor of London. The content of the tweet hardly matters and is anyway open to different interpretations. But what does the president think he is doing? Imagine if the British prime minister had tweeted her disapproval of the mayor of New York on the day after 9/11. It would not have happened, and nor should Trump's irruption into the aftermath of the London terror attacks.

The problem with these tweets isn't that they irritate his enemies but that they empower them. Trump's tweeting isn't always harmful, but it often is. And his best moments, when you think back over his presidency, come when he sticks to his script. He think he is good at winging it because he won the presidency doing so. But that was campaigning, and this is governing, which is a very different thing. It's past time for the president to understand this.

The question he needs to answer for himself is whether he is more in love with blasting off his thoughts to the world in utterly ungoverned fashion or actually succeeding in getting his agenda on to the statute books of the nation.

There's an old saying: Fools rush in where angels fear to tread. If he cares about accomplishing his agenda, Trump will get off Twitter.