He sides with the leader of a foreign country against the president of the US on an issue of great diplomatic significance. Cantor, of course, directly supports Israel's continued occupation and colonization of the West Bank and uncontrolled settlement construction. And just as significant as Cantor's direct attempt to undermine his own president by siding with a foreign leader is that foreign leader's agreement to meet with him in order to advance the cause of Greater Israel.
There are no parallels with this kind of direct undermining of the president on foreign policy that I can think of. Am I wrong?