The 25 Amendment
The Speaker of the House would become president if the president and VP were incapacitated at the same time.
The Senate can remove Federal officials from office. The Senate is responsible for initiating an impeachment of a President of the United States. The Senate can also vote to have a member of the Senate removed for misconduct.
Legislative over the execitive
We now have a black president and we had white ones before.
The President before Abraham Lincoln was James Buchanan.
The Vice President
President Bush
If the President dies and the Vice President takes over, the Vice President becomes the President. The Vice Presidency position would then be vacant and would need to be filled according to the constitutional process.
THe vice-president can temporarity or permanently assume the powers of the President. The 25th amendment gives the process for transferring the power and restoring it when appropriate.
One is the impeachment process. The House has the exclusive power to impeach a president, and then the Senate tries the president. Another is the over-ride of a presidential veto.
They have a career job but the President has a limited term of office.