From the Document: "For the second time in just over a year, the House of Representatives has voted to impeach President Donald J. Trump. The House previously voted to impeach President Trump on December 18, 2019, and the Senate voted to acquit the President on February 5, 2020. Because the timing of this second impeachment vote is so close to the end of the Trump Administration, it is possible that any resulting Senate trial may not occur until after President Trump leaves office on January 20, 2021. This possibility has prompted the question of whether the Senate can try a former President for conduct that occurred while he was in office."
CRS Legal Sidebar, LSB10565
Congressional Research Service: https://crsreports.congress.gov/