Why it matters: John Sullivan, a respected diplomat who President Biden has, so far, retained from the Trump era, is at the center of one of the most important early tests of Biden's resolve. Russia's foreign ministry announced Friday it would expel 10 American diplomats and bar current officials, such as Attorney General Merrick Garland, from visiting Russia. But the Russians didn't expel Sullivan. Instead, the Kremlin summoned him to meet with a top foreign policy official, Yuri Ushakov, who recommended he go back to Washington for consultations with Biden officials. Sullivan's view, according to people familiar with his thinking, is that if Putin wants him to leave, he'll have to force him.