Final answer:
A two-thirds vote by the senators present at the trial is necessary for conviction in an impeachment trial conducted by the Senate, and the Chief Justice presides when the President is tried.
Step-by-step explanation:
For a conviction in an impeachment trial in the Senate, a two-thirds vote is required. Specifically, two-thirds of the senators present during the trial must concur in order to convict the accused official. When the President of the United States is on trial, the Chief Justice of the U.S. Supreme Court presides over the proceedings. The Senate has the sole power to try all impeachments, and upon conviction, the person can be removed from office and potentially barred from holding future federal positions. However, the Senate does not have the authority to impose additional punishments; those must come from court proceedings outside of the impeachment process.