#25thamendent: Here is what it says:

What the law says

The language of the amendment says if the vice president and either a majority of the executive Cabinet or a review body appointed by Congress declare in writing that the president is unfit for office, then the vice president immediately becomes the acting president.

But the law also gives the sitting president, Trump in this case, the chance to argue that he is fit for office.

In the case of competing arguments about the president's ability to lead, "Congress shall decide the issue," the amendment says. For the vice president to assume the power of the presidency, two-thirds of both the House of Representatives and Senate must vote in favor of that outcome.

If Congress does not have the sufficient majorities in both parties in favor of rescinding the president's power, then he remains in power.