So, Mr. Edwards asks, "What happens to the president-elect if convicted of a crime before taking the oath of office? After?" Great question, because it cuts to a constant theme of this presidential election - most Americans think one or the other candidate, or both, is prone to criminal behavior.
Sigh. This election is making me old.
Okay, let's say a president-elect, that is to say a president already voted into office by the Electoral College, is believed by a sufficient number of people to be guilty of some crime or another - they're going to have to be impeached. To clarify why let me respond by quoting the Constitution. First, Article I, Section 2:
The House of Representatives shall chuse their Speaker and other Officers; and shall have the sole Power of Impeachment.
Second, Article I, Section 3:
The Senate shall have the sole Power to try all Impeachments. When sitting for that Purpose, they shall be on Oath or Affirmation. When the President of the United States is tried, the Chief Justice shall preside: And no Person shall be convicted without the Concurrence of two thirds of the Members present.
Judgment in Cases of Impeachment shall not extend further than to removal from Office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law.
Third, the final clause of Article II, Section 2:
The President . . . shall have Power to grant Reprieves and Pardons for Offences against the United States, except in Cases of Impeachment.
Fourth, Article II, Section 4:
The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.
And finally, Article III, Section 2, Paragraph 3:
The Trial of all Crimes, except in Cases of Impeachment, shall be by Jury; and such Trial shall be held in the State where the said Crimes shall have been committed; but when not committed within any State, the Trial shall be at such Place or Places as the Congress may by Law have directed.
That is the sum and total found in the Constitution on the subject of impeachment. It isn't much but it lays out the gist of things.
First, while he or she holds office a president, or presumably president-elect, must be impeached and the impeachment confirmed with a 2/3rds majority in the Senate. He or she is not eligible for trial in the judicial branch, according to all the normal laws and methods of the US government, until they leave their position as an officer of the United States. Upon impeachment, however, the president can be tired for, well, anything they may be formally charged with - including but not limited such crimes as may be deemed appropriate for impeachment, including treason, bribery, high crimes, and high misdemeanors.
Put simply, in order to buffer the mechanisms of government from a criminal proceeding against a sitting officer, the Constitution requires that political leaders deem the threat of the officer's misconduct be so great that they are willing to stake their reputations on that officer's removal and, of course, must be able to achieve a high level of bipartisanship (again, check that supermajority requirement out). Then, should impeachment be carried out, the newly private citizen simply is tried according to the common law and procedure of the Union.
Easy, peasy, lemon-squeezey.