Actually all he had to do was NOTIFY Congress. He then had 45 days. . . .
Yourfinal point here is still undecided. Did he use the bargining chip for his own personal benefit or was there a national interest? Or both?
Maybe Chris Kern could chime in and fix everything I screwed up here 
I'm no expert on the interpretation of the
Impoundment Control Act, but the U.S. Government Accountability Office
decision of January 16 notes that the law
. . . authorizes the deferral of budget authority in a limited range of circumstances: to provide for contingencies; to achieve savings made possible by or through changes in requirements or greater efficiency of operations; or as specifically provided by law. . . . No officer or employee of the United States may defer budget authority for any other purpose.
If President Trump withheld the congressionally-appropriated assistance to Ukraine for policy reasons, as he and his defenders have stated―e.g., because he was concerned about corruption in Ukraine or wanted to ensure that European governments were incurring their share of the burden of support to that country―that apparently would be a violation of the statute, which is what the GAO concluded in its decision. In other words, the 45-day notification requirement for
authorized deferrals would not apply.
If his request for "a favor" from President Zelensky would have conferred a political benefit to Trump, regardless of whether he may have had another, independent, policy rationale, that would appear to be a violation of
52 USC §30121: "It shall be unlawful for . . . a person to solicit . . . [a contribution or donation of money or other thing of value] from a foreign national."
Whether either of these violations of law justifies removal from office pursuant to the constitutional provisions for impeachment is, of course, a decision for the Senate to make.
Addendum:
I did not intend to imply in my initial version of this post that a violation of a statute is a prerequisite for impeachment. There is nothing in the U.S. Constitution that requires a statutory violation, and (the unorthodox claims of Alan Dershowitz notwithstanding) the surviving records of the constitutional convention and the common law of "high crimes and misdemeanors" clearly indicate that a crime is neither required nor sufficient to justify removal from office.
