Qatar’s feud with its neighbors is bad for the U.S.

A family feud has broken out in the Arabian Gulf, threatening a crucial American military base, and the best thing the U.S. can do is act as mediator. Unfortunately, that is not President Donald Trump’s preferred role — especially when he’s on Twitter.

A coalition of Arab states, led by Saudi Arabia and including Egypt and the United Arab Emirates, have cut diplomatic relations and barred travel and commerce with Qatar. That small nation, the world’s richest per capita, has spent years trying to become a player in regional politics, often to the irritation of its Gulf neighbors.

Qatar opposed the coup in Egypt that installed a military government, for example, and supports Islamist movements, while the governmentsponsored TV network, Al Jazeera, is frequently critical of the Gulf monarchies. These are among the issues that led those same Arab neighbors to temporarily cut off relations in 2014. The biggest current issue is Qatar’s relationship with Iran, which they consider an existential threat.

The situation reached a crisis point last month when Qatar’s emir, Sheikh Tamim bin Hamad Al Thani, phoned Iranian President Hassan Rouhani to congratulate him on his re-election. The official state news agency also published a story with quotes from the emir both favorable to Iran and critical of Trump — remarks the Qatari government denies, and which the U.S. is said to be investigating as a possible plant by Russian hackers.

Regardless, Trump tweeted on Tuesday that his trip to Riyadh last month, when he sided firmly with the Arab states against the Tehran government, is “already paying off.” Qatar’s funding of extremism, he tweeted, was the reason for its isolation.

But Qatar is not the only Gulf state that funds terrorists, which Trump knows. More to the point, Trump should be working to reconcile the monarchies, to ensure that the winners in all this aren’t Iran, the terrorists and Russia, which has volunteered to play peacemaker.

Qatar’s wealth depends on an underwater natural gas field it shares with Iran, so it has to maintain at least cordial relations. Some of its other “offenses” are even more defensible, such as Al Jazeera’s subjective yet uncensored news coverage.

Most important, Qatar hosts the U.S.’s main Middle Eastern airbase and the forward headquarters of the Pentagon’s Central Command. This is the nerve center of the wars against Islamic State and the Taliban — and all officials from the boycotting countries have been yanked away on the eve of a climactic battle in Raqqa, Syria.

It is futile, at this point, to advise Trump not to use Twitter. But someone has to be able to persuade him not to undermine his own administration and U.S. interests. Pushing Qatar into the arms of the Kremlin and Tehran would be a colossal mistake. The president, or at least Secretary of State Rex Tillerson — who as former CEO of ExxonMobil has deep ties to most of the players — should be working to heal this rift, not widen it.

Qatar opposed the coup in Egypt that installed a military government, for example, and supports Islamist movements, while the governmentsponsored TV network, Al Jazeera, is frequently critical of the Gulf monarchies