Oh there was ALOT to it. Even without the treason..Reagan violated the Constitution and the Law. The logical conclusion to the Iran Contra investigation was impeachment and removal from office. But Democrats being Democrats in the face of a popular President and with the Nixon debacle at their heels opted to make the President go on National tv and declare that he lied.
Which he did. And not very convincingly. He said he didn't "remember".
Well, there were a whole lot of problems with that statement.
Keep in mind, Lawrence Walsh never brought charges against Reagan or Bush personally. He prosecuted North and Poindexter, not for trading arms for hostages (which, by the way, wasn't illegal) or even diverting funds to the contras (which might have been, but there was no evidence Reagan knew about that) but for lying to Congress. And although he won convictions for that, they were thrown out by higher courts because the two men had received immunity and he introduced inadmissable testimony to prove his case.
You See, Congress had given them immunity hoping they would break bad on Reagan. Instead, they admitted the possibly illegal Contra part of the deal was entirely their idea, and they kept Reagan out of it to protect him from liability.
Eventually, Walsh ended up prosecuting Cap Weinberger for lying because he said he hadn't kept a diary, but in fact he had taken meeting notes. (Weinberger, for those playing along at home, had opposed the arms transfer deal.)
I'm not sure why the "Nixon Debacle" would have discouraged them. They got a sitting president to resign, one who had been elected by 60% of the electorate. The padded their congressional majorities in 1974 and took the white house in 1976. Nixon was a big win for them. They'd have been happy to repeat it if they could.
The reason they couldn't was, at the end of the day, he wasn't acting out of selfish reasons. He was acting out of the best interest of the country, and to save American lives.
He wasn't acting out of personal gain like Clinton was. That's what made what Clinton did impeachable.