The Washington Post reports:

President Biden’s decision last month to help Ukraine obtain F-16 fighter jets marked another crossing of a Russian red line that Vladimir Putin has said would transform the war and draw Washington and Moscow into direct conflict.

Despite the Russian leader’s apocalyptic warnings, the United States has gradually agreed to expand Ukraine’s arsenal with Javelin and Stinger missiles, HIMARS rocket launchers, advanced missile defense systems, drones, helicopters, M1 Abrams tanks and, soon, fourth-generation fighter jets.

A key reason for brushing aside Putin’s threats, U.S. officials say, is a dynamic that has held since the opening days of the war: Russia’s president has not followed through on promises to punish the West for providing weapons to Ukraine. His bluffing has given U.S. and European leaders some confidence they can continue doing so without severe consequences — but to what extent remains one of the conflict’s most dangerous uncertainties.

“Russia has devalued its red lines so many times by saying certain things would be unacceptable and then doing nothing when they happen,” said Maxim Samorukov, a Russia expert at the Carnegie Endowment for International Peace. “The problem is that we don’t know the actual red line. It’s in one person’s head, and it can change from one day to the next.”

U.S. officials say managing the risk of escalation remains one of the most difficult aspects of the war for Biden and his foreign policy advisers. When deciding what new weapons systems to provide Ukraine, they focus on four key factors, officials said.

“Do they need it? Can they use it? Do we have it? What is the Russian response going to be?” said a senior State Department official. [Continue reading…]