What would be the reaction in the USA if Iran invaded Canada or Mexico in response to a non-existent threat?

How would the USA act if Iran had invaded and occupied Canada or Mexico and was arresting U.S. government representatives there on the grounds that they were resisting the Iranian occupation (called "liberation," of course). Imagine as well that Iran was deploying mive naval forces in the Caribbean and issuing credible threats to launch a wave of attacks against a vast range of sites -- nuclear and otherwise -- in the United States, if the U.S. government did not immediately terminate all its nuclear energy programs (and, naturally, dismantle all its nuclear weapons). Suppose that all of this happened after Iran had overthrown the government of the U.S. and installed a vicious tyrant (as the US did to Iran in 1953), then later supported a Russian invasion of the U.S. that killed millions of people (just as the U.S. supported Saddam Hussein's invasion of Iran in 1980, killing hundreds of thousands of Iranians, a figure proportinonately comparable to millions of Americans). Would the USA watch quietly and do nothing?