Sure. But, it recent history if a Dem coalition sent a letter to Moscow to warn them that any Nuclear agreement would be changed with the next Pres, the GOP would have went ape. Nor did the Dems do that, they allowed Reagan to negotiate.
Reagan was an American loyal to America. (And the Senate still had the constitutional last word on anything he negotiated anyway, just as now ). Best,
I guess you forgot about Teddy Kennedy asking Andropov to help defeat Reagan by promising to help him discredit Reagan.
Maybe you remember John Kerry negotiating with the Viet Cong in the Paris peace accords while still a member of the Naval Reserve. Kerry was and is a scumbag traitor who lied profusely before J William Fulbright's committee but since he was not sworn in it was ok to lie his @ss off.
Maybe you remember The 'Dear Comandante' letter (1984) - Political Warfare