Original intent?
The Founding Fathers put the amendment process into the US Constitution. Amending the Constitution IS ORIGINAL INTENT.
They didn't intend for the Constitution to become so outdated. They assumed that people would change with the times, instead of being stuck with archaic systems.
However, you're very much getting stuck on something which isn't worth getting stuck on.
However, I'm going to talk about what other ways there are.
Try this. Trump somehow manages to get enough Congressmen on his side, who won't impeach him. He gets the Supreme Court to say anything he does as President is fine. He gets the Supreme Court to back him up with things.
Let's see his US citizenship for all people born in the US get knocked down by the Supreme Court. All of a sudden he's gained power over the Constitution WITHOUT the amendment process.
What next? He could just keep pushing, some of the Supreme Court justices are very easy to BRIBE, like Thomas, if he gets a Supreme Court that's on his side, willing to bend the rules, ANYTHING is possible.
Checks and balances are in place, but not if the people who are the checks and balances are with him.