Treason?

[Oberon]

I wouldn't have said it was treasonous. The people actually doing the negotiation will probably take as much notice of it as a cow takes of a daffodil. It's just fuel for both sides who oppose the deal and little else.
It might make things after the negotiations are concluded a little difficult, but it won't have much effect on the actual negotiations themselves.
But I'd say definitely not treasonous, although you're right that the Republicans would probably cry Treason if the Democrats did something like this, but the Senate and Congress are well within their rights to express their opposition to the Presidents actions in any manner they see fit, it's part of the checks and balances in the system.
Of course, when neither side are willing to compromise to get things done then you wind up with gridlock in the political system. That's a downside, but equally having a President rule with nothing to counter him or her is also a major downside.