1) the president and other federal officials may be impeached
a) for "treason or other crimes that affect the entire nation" under article i of the constitution
b) "only upon suspicion of treason or resignation without notice" under article i of the constitution
c) ''only after removal from office for charges related to treason" under article ii of the constitution
d) for "treason, bribery, or other high crimes or misdemeanors" under article ii of the constitution

I believe the answer is: d) for "treason, bribery, or other high crimes or misdemeanors" under Article II of the Constitution

Here is the full text in the article of II
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.

The impeachment would be initiated by the senates of united states. But they first have to obtain a solid proof beyond reasonable doubt before they can begin the impeachment process.