When Bush was president, if he died, the vice president, Dick Cheney will become president (or Dan Quayle if speaking of George Bush Sr.)
If Bush dies now, Barack Obama will remain president.
If he dies in office, then Dick Cheney becomes President.
The vice president
The Vice President
The vice-president
the vice president.
If both die then the Speaker of the House becomes president
The vice-president becomes the president.
If Obama dies in office, his vice President, Joe Biden, becomes the next President.
President pro tempore of the Senate becomes President.
vice president, & if he dies, the speaker of the house
The Vice President of America.
When the president dies the vice president becomes the president