(CNN) In the long saga of Donald Trump's tax returns, Monday was a very important day.

A three-judge federal appeals court ruled that Trump cannot claim presidential immunity to avoid eight years of his tax returns being subpoenaed by a grand jury. Trump lawyer Jay Sekulow immediately released a statement saying that Trump will appeal the ruling. All of which means this case is probably going to wind up in front of the Supreme Court.

Which is what we expected when this all began. People weren't going to stop trying to get the President's tax returns. And the President made a decision a long time ago that he wasn't handing them over without a major fight.

What is most interesting, however, is what the appeals panel ruled -- and whether that complicates the Supreme Court's presumed decision whether to hear the case.

"The only question before us is whether a state may lawfully demand production by a third party of the President's personal financial records for use in a grand jury investigation while the President is in office," wrote the judges, adding: "We hold that any presidential immunity from state criminal process does not bar the enforcement of a subpoena."

Read More