Over the course of three and a half months, Mr. Biden made three critical decisions about how to handle Russia’s provocations, according to interviews with more than a dozen senior administration officials and others who requested anonymity to discuss confidential meetings. Early on, the president approved a recommendation to share intelligence far more broadly with allies than was typical, officials said. The idea was to avoid disagreements about tough economic sanctions by ensuring that everyone knew what the United States knew about Mr. Putin’s actions.

Mr. Biden also gave the green light for an unprecedented public information campaign against Mr. Putin. With the support of his top intelligence officials — and with a promise to protect the intelligence agencies’ “sources and methods” — the president allowed a wave of public releases aimed at preventing Mr. Putin from employing his usual denials to divide his adversaries.

And when it became clear this year that Mr. Putin was continuing to build up forces at Ukraine’s border, the president approved sending Ukraine more weapons, including Javelin anti-tank missiles, and deploying more troops to other countries in Eastern Europe as a show of solidarity with Ukraine and to reassure nervous allies on NATO’s eastern flank.