the "Impoundment Control Act" does not forbid the president from withholding funds appropriated by congress. It puts limits on and requirements for withholding funds. It is not against the law and certainly not in the constitution for a politician to get help from a foreign national in an election. They are prohibited from getting help for money, like for instance paying for a dossier, under the FEC laws and regulations. Trump never publicly asked Russia, China or Ukraine to get involved in any election. That is all dreamworld stuff.