From my 2004 LRC post:
A French-German Tulane law student acquaintance of mine (he speaks nine languages–I only speak about 0.7), Frederic Sourgens, sent me his Inn of Court brief where he argues for the impeachment of President Jefferson for undertaking the unconstitutional Louisiana Purchase. A bit rough, but fun… Download file. After 30 pages of legal reasoning, it concludes: “President Jefferson must be removed from office because of his blatant disregard of the Constitution constituting a high misdemeanor of state and high treason against the United States.“
Since the Senate ratified the treaty twenty four to seven (more then the 2/3 required) then I see no problem with what Jefferson did. All treaties involve the President agreeing to things that he alone does not have the power to do, that is why they are treaties and why they must be ratified by the Senate which does have the power. At the very least if you are going to impeach Jefferson then you also have to impeach twenty four senators, which would make impeachment hard since they would have to impeach themselves or have their respective states replace them.
If Congress passed a law banning non-state owned media companies, and the President signed the bill, that would not change the fact that the President should be impeached for signing the law.