[Referring to
52 USC §30121: "It shall be unlawful for . . . a person to solicit, accept, or receive [a contribution or donation of money or other thing of value] from a foreign national."]
Doesn't this still leave us with someone needing to prove that the request for a favor was actually for Trumps personal gain and not something that might be in the national interest.
In a proceeding before the Federal Election Commission, or a subsequent appeal of an adverse FEC decision to a federal court, probably not. It is sufficient that the contribution or donation or other thing of value came from a foreign national and would have conferred a political benefit.
However, in a Senate trial of the impeachment, some of President Trump's more ardent defenders might try to argue that. It's a weak argument, in my opinion, especially since every senator is aware that U.S. presidents don't ask foreign heads of state or government to initiate investigations of U.S. citizens. (In those rare instances where federal agencies require assistance of that kind―almost always involving intelligence or counterintelligence matters―there are established channels for U.S. agency officials to submit official requests to their international partner agencies.)
If I were defending Trump, I would stipulate that, yes, he violated the federal election law, but argue that the violation does not rise to the level of an abuse of power (i.e.,
high crime and misdemeanor) sufficient to justify removal from office.
Of course, if the impeachment managers from the House of Representatives can establish that Trump withheld congressionally-appropriated assistance to Ukraine improperly―either to apply leverage on the Ukrainian president or in violation of federal law―the 52 USC §30121 violation would be rather trivial by comparison.