Are there any words that start with X and have to do with the American President?

not really. There are not many Words that start with "x" and it would a huge stretch to tie any of them to an American President. He is the best I can do:

X-rays were invented in 1895 while Cleveland was President, If they had been around in 1881, they might have saved Garfield's life.

Washington was not exactly a xenophobe but he was leery of foreign entanglements.