Are there other issues?

Yes. After the recent suspensions of non-immigrant visas shook Turkey’s financial markets on Monday, the two sides signaled a willingness to ease tensions, but an American official warned, “We haven’t hit bottom yet.”

Mr. Erdogan is worried about the impending trial in the United States of Reza Zarrab, a Turkish-Iranian gold dealer accused of violating sanctions on Iran, because he is connected to a corruption scandal that almost brought down Mr. Erdogan’s government in 2013. The Turkish leader is further incensed by America’s indictment of 15 of his personal bodyguards after a brawl with protesters in May during his visit to Washington. The two countries are at odds over American support for Kurdish fighters in Syria; Turkey considers those fighters to be terrorists allied with a Kurdish group in Turkey that has waged an insurgency there for 30 years. Washington is concerned that Turkey is distancing itself from NATO, as evidenced by its pro-Russia tilt in the Syrian war and its bid to buy a Russian missile defense system that cannot be integrated with NATO’s defenses.

Why can’t the U.S. simply kick Turkey out of NATO?

NATO has no provision for that, and besides, the United States wants Turkey to stay. Having an influential ally in the Mideast and access to the region is critical. But Mr. Erdogan’s anti-Western behavior is sowing deep mistrust about his commitment to an alliance that is supposed to be based as much on the common values of “democracy, individual liberty and the rule of law” as on a common military defense. So NATO experts are debating Turkey’s future and the wisdom of keeping the tactical nuclear weapons at Incirlik.

Doesn’t it help the U.S. to have nuclear weapons in Turkey?

No. Experts have long worried about the weapons’ security. During the coup attempt last summer, the Turkish government locked down the base for 24 hours, and the electricity was cut. Incirlik is near Syria, with its warring extremist forces. Mr. Erdogan’s anti-American behavior and his drift toward Russia have heightened anxiety.

The weapons were deployed decades ago as proof of America’s commitment to Turkey’s security but are symbolic. No one expects them to be used, and no planes at Incirlik can deliver them. The security commitment is better demonstrated in other ways. When the United States withdrew nuclear weapons from Greece, also a NATO ally, in 2001, it sold Greece F-16 fighter jets. If it becomes necessary to defend Turkey, America can use conventional weapons.

Can you really just move 50 or more nuclear weapons?

It’d be smart to move the weapons before Turkish-American relations collapse. A withdrawal would probably best be done quickly and covertly after the American-led coalition captures Raqqa, Syria, from the Islamic State.

Would this be a wake-up call to Mr. Erdogan? Or simply end the two nations’ alliance?

NATO is a consensus organization, and Turkey could make mischief by thwarting its decision-making. It could also withdraw from the alliance. But Turkey has prospered as a NATO member. That means it is likely to be the big loser if it forsakes the West for, say, closer ties with Russia. Mr. Erdogan needs to face up to the reality that the problem, like the provocations, are not NATO’s but his. He still has time to mend his ways.