Quick: How could a sitting U.S. president be legally removed from office? Most people have heard of impeachment, a power granted to (and rarely used by) the U.S. Congress. But there’s also the 25th amendment to the U.S. Constitution, which provides an avenue for a president to be removed under extraordinary circumstances by his or her own leadership team. Critics of President Donald Trump have cited the amendment approvingly, even wishfully, over the past two years while reviewing what they consider his erratic behavior. More recently there are indications that deploying the amendment has even been discussed within Trump’s own government.

1. What does the 25th amendment say?

It provides that a president can be removed if the vice president and a majority of the cabinet determines he or she is “unable to discharge the powers and duties” of the office. If the president contests the finding, and the vice president and cabinet persist, Congress can order the president’s removal by a two-thirds vote in both chambers. The amendment also clarifies that the vice president is the successor if a president leaves office in midterm, and that the vice president becomes acting president when, say, a president undergoes major surgery.

2. Why does the 25th amendment even exist?

To address some questions about presidential and vice presidential succession that the Constitution didn’t specifically answer. For instance, when President William Harrison died in office in 1841, there was a debate over whether Vice President John Tyler would become acting president, or president, or officially remain vice president. (Tyler decided on his own to have a judge administer the presidential oath of office.) The 25th amendment was introduced in Congress, and ratified by the requisite three-quarters of U.S. states, after the 1963 assassination of President John F. Kennedy. In the immediate confusion following the shooting of Kennedy, there were tense questions about who would run the country should he survive but only in a semiconscious or otherwise grievously wounded condition.

3. Has the 25th amendment been used before?

Never to remove a sitting president, but twice to fill a vacant vice presidency. (Before the amendment took effect, the U.S. occasionally went long periods without any vice president.) In 1973, after Spiro Agnew was forced to resign because of tax-evasion charges, President Richard Nixon nominated Representative Gerald Ford to become vice president. He was approved by the House and Senate. After Nixon resigned the following year, Ford became president and nominated Nelson Rockefeller, a former governor of New York, as vice president. He was confirmed by Congress.

4. Why is the 25th amendment coming up now?

The New York Times and ABC News reported that the deputy attorney general, Rod Rosenstein, last year discussed recruiting cabinet members to invoke the amendment to remove Trump from office. (Rosenstein denied the account and said in a statement to the Times that he sees “no basis” to invoke the amendment.) Weeks earlier, on Sept. 5, the Times published an op-ed by a person identified only as “a senior official in the Trump administration” who wrote, “Given the instability many witnessed, there were early whispers within the cabinet of invoking the 25th amendment, which would start a complex process for removing the president. But no one wanted to precipitate a constitutional crisis. So we will do what we can to steer the administration in the right direction until — one way or another — it’s over.”