It was known well before Trump had even entered the primary in 2016 that he had obtained major loans from DeutscheBank, which has close ties to the Kremlin, and that Trump had been negotiating to build
a large structure in Moscow. Whereas it is not illegal for a private citizen to have major financial entanglements in a foreign nation, holding major financial leverage over Trump and/or his family could give a foreign power undue influence over decisions being made by our president, especially in the case of an individual who so obviously places his own interests above those of the nation he is supposedly serving.
Even the redacted Mueller report in Part One describes widespread and systematic efforts on the part of Russia to sway the election in Trump’s favor. That insufficient evidence was found to charge CRIMINAL conspiracy on the part of Donald Trump was due to the many instances of Obstruction of Justice described in Part Two of the report. Even if such evidence had been found, Mueller would have been restrained from an actual indictment of the President by the same DOJ policy that – very unfortunately, IMHO – restrained him from indicting the president for the many instances of Obstruction of Justice as described in Part Two.
Because DOJ policy restrained Mueller from indicting the president, it is now up to Congress to use its additional powers of subpoena to complete the investigation of the Drümpf crime family’s many possibly illegal activities and to issue indictments and/or initiate impeachment proceedings against the president if warranted.