What happens if Trump is no longer in office during impeachment trial?

The House of Representatives voted to impeach President Trump for a historic, second time on Wednesday. By the time the Senate trial concludes, Mr. Trump will already be out of office. CBSN legal analyst and New York Law School professor Rebecca Roiphe joins CBSN’s Lana Zak to discuss the constitutionality of impeaching someone after leaving office and what comes next. Source