Has the us faced a constitutional crisis?

Yes, here's a few

- The death of President William Harrison. People weren't sure whether the Vice President (John Tyler) was supposed to become an Acting President or a permanent President. John Tyler successfully made sure that it was permanent.

- The Nullification Crisis, where South Carolina announced that it would override a decision of the Federal Government. In the end, SC was forced to comply with the law and it became established the Federal Government was in charge.

- The secession of the Confederate States. The Constitution had been silent on whether this was allowed. Of course, it triggered a civil war. Since the Unionists won the war, it is now accepted that secession isn't possible.

- The 1876 Presidential election.