What should be done if the President is mentally ill?

What a disrespectful topic to be posted on a site primarily used by US military personnel. What intrigues me the most about this post is the use of the word "Regime" to describe the President and his Cabinet. Simply remarkable this post would circulate, however, this is the United States of America and everyone's opinion is allowed to be heard, viewed and written in a forum like this; sad at times but true.

Guess we will find out.

That is what the 25th amendment is for.

I'm sure the democrats already asked this question during President Lincoln's time in office.

Nothing - Being mentally ill is not an impeachable offense. Unless the president does something so outrageous that 2/3 of the senate will convict him on an article of impeachment...there is nothing that can be done. Using our present president as an example, I cannot see any possible way that will ever happen. Being impeached does not really mean much - unless you have the senate prepared to go along with the house - it is also pretty much a waste of time. However, just because something is a waste of time does not stop the persons in Washington, DC, from doing it.

Support him he is no more mentally ill than most of the commanders we have in the military today and a hell of a lot less than most

Stop listing to the Socialists in Congress and the left-wing propaganda specialists that support them. We finally have a president that is making every attempt to keep his promises. He is doing this with out much help from Congress and doing everything to stay within the confines of his Constitutionally defined powers, something that obama didn't do!

You're off base, LT. The fact that you cite three NYT articles supporting your position demonstates your bias. That being said, I don't see what your post has to do with the military per se. It belongs in the Letters to the Editor section of your local newspaper.

The 25th Amendment reiterates what is stated in Article 2, Section 1: that the Vice President is the direct successor of the President. He or she will become President if the President cannot serve for whatever reason. The 25th also provides for a President who is temporarily disabled, such as if the President has a surgical procedure or if he or she become mentally unstable.
The original Constitution provides that if neither the President nor Vice President can serve, the Congress shall provide law stating who is next in line. Currently that law exists as 3 USC 19, a section of the U.S. Code. This law was established as part of the Presidential Succession Act of 1947. There, the following line of succession is provided:
No. Office Current officer
1 Vice President Mike Pence (R)
2 Speaker of the House of Representatives Paul Ryan (R)
3 President pro tempore of the Senate Orrin Hatch (R)
4 Secretary of State Rex Tillerson (R)
5 Secretary of the Treasury Steven Mnuchin (R)
6 Secretary of Defense James Mattis (I)
7 Attorney General Jeff Sessions (R)
8 Secretary of the Interior Ryan Zinke (R)
9 Secretary of Agriculture Sonny Perdue (R)
10 Secretary of Commerce Wilbur Ross (R)
11 Secretary of Labor Alex Acosta (R)
12 Secretary of Health and Human Services Eric Hargan (R)[a]
Acting
13 Secretary of Housing and Urban Development Ben Carson (R)
– Secretary of Transportation Elaine Chao (R)[b]
14 Secretary of Energy Rick Perry (R)
15 Secretary of Education Betsy DeVos (R)
16 Secretary of Veterans Affairs David Shulkin (I)
17 Secretary of Homeland Security Elaine Duke (I)[a]
Acting

Well, if you feel your Commander in Chief is mentally ill and are still serving use your chain of command open door policy.