No. It was not treason.
Here is Fred Barbash at The Washington Post: But nothing Trump did in Helsinki and nothing he has done otherwise that anyone knows of are likely to qualify as treason, at least by its legal definition.
“Treason against the United States,” says Section 3, Article III, of the U.S. Constitution, “shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort.” It’s the only crime explicitly defined in the nation’s founding charter. The framers clearly wanted it used sparingly, declaring that “no person shall be convicted of treason unless on the testimony of two witnesses to the same overt act, or on confession in open court.” The absence of an “overt act,” among other factors, helped former vice president Aaron Burr win an acquittal in 1807 in the most famous treason trial of all, after he was accused of plotting to set up his own empire in the west.
Trump and treason? “No, not at all,” Carlton F.W. Larson, an expert on the subject at the UC Davis School of Law, told The Washington Post.
“It’s funny,” he said, “because people keep asking me if it’s treason yet. He could hand the nuclear codes over to Putin and it wouldn’t be treason. This isn’t anything as bad as that. Groveling in front of a foreign leader, putting the interests of a foreign country ahead of the United States, displaying horrific judgment in foreign policy — none of those things are treason.”
Trump would have to be participating in waging war against the United States or giving “aid and comfort” to the nation’s enemies to be vulnerable to treason charges, either in a court or an impeachment proceeding.
Problem one: The United States is not at war.
Read the entire piece here.