Iranian forces have shot or locked up antigovernment protesters, provided Russia with drones for its war in Ukraine and, some Western intelligence agencies suspect, may be negotiating to produce missiles as well for Russia’s depleted arsenal. The United States accused Iran on Tuesday of once again violating Iraqi territory to conduct attacks in the Kurdistan region.

A new era of direct confrontation with Iran has burst into the open. Its emergence was hidden for a while by more dramatic events — including the Ukraine invasion and rising U.S. competition with China — and negotiations with Tehran dragged on, inconclusively, for 18 months.

Now, Mr. Biden’s hope of re-entering the United States into the deal with Iran that was struck in 2015, and that President Donald J. Trump abandoned, has all but died. Negotiations halted in September, and in recent weeks Mr. Biden has imposed new sanctions on Iran and expressed support for protests that Iran’s hard-liners have portrayed as a mortal threat.

At the White House, national security meetings on Iran are devoted less to negotiation strategy and more to how to undermine Iran’s nuclear plans, provide communications gear to protesters and interrupt the country’s supply chain of weapons to Russia, according to several administration officials.

[Who says an old dog can’t learn new tricks? I commend President Klain for his belated recognition of reality. — Ed]