Constitutional scholar Mark Tushnet describes the norm: “The House of Representatives should not aggressively carry out an impeachment unless…there is a reasonable probability that the impeachment will result in the target’s removal from office.” Since removal requires a two-thirds vote in the Senate, this means that impeachment should have at least some bipartisan support. After Johnson’s impeachment in 1868, there were no serious congressional efforts to impeach the president until the Nixon scandal more than a century later.
