Where in the US Constitution does it have a “petition” clause?
It is amazing what kind of crap the White House uses a government site for.
Not that I think these petitions are any use, but to answer your question:
Amendment 1: Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
So use their own tactics against them. Lefties hate it when you Alinsky them.