Final answer:
If the President dies, the Vice President becomes President as outlined by the 25th Amendment. If the President-elect dies before taking office, the Vice President-elect becomes President. Congress may determine succession if neither is qualified.
Step-by-step explanation:
When the President of the United States dies, resigns, or is removed from office, the Constitution provides clear guidance on succession. According to the 25th Amendment, Section 1, in the event of the President's death, the Vice President shall become President. Moreover, if the President-elect dies before their term begins, the Vice President-elect becomes President, as indicated in the 20th Amendment. In the circumstance where neither the President-elect nor the Vice President-elect have qualified, Congress may decide by law who shall then act as President.
The line of succession beyond the Vice President is further delineated by the Presidential Succession Act of 1947. The Act places the Speaker of the House of Representatives next in line, followed by the President pro tempore of the Senate, and then the eligible heads of federal executive departments, beginning with the Secretary of State.