You can if you change the definition of libel (or terrorism) to be āanything that negatively affects an ultra rich personā. Which is what is happening before our very eyes.
You can. You can sue for any reason that you can dream up. True, a lot of those suits would get thrown out on a motion for summary judgement, but a libel suit would likely pass the test of a prima facie valid case, and the case would proceed. Now, if the facts don't support it, then you'd lose, but if you have a lot more money than the defendant, you can use procedure to bury them financially.
It's one of the major flaws in the U.S. legal system, and anti-SLAPP laws are far too weak, since they usually rely on the defendant to try to enforce them.