Occam's razor (or Ockham's razor) is a principle from philosophy. Suppose there exists two explanations for an occurrence. In this case the one that requires the smallest number of assumptions is usually correct. Another way of saying it is that the more assumptions you have to make, the more unlikely an explanation.(Wikipedia)
1. Russia illegally intervened in the U.S. election with the goal of electing Donald Trump, and Donald Trump welcomed that help; 2. Donald Trump often makes decisions which benefit Russia and are detrimental to American interests: e.g.-withdrawal of American troops from Syria, pushing for Russian re-inclusion in the G7, allowing Russia to gain greater military power in Syria; 3. Donald Trump, and only Donald Trump, as POTUS, has held secret talks with Vladimir Putin the content of which has never been revealed to other officials in the U.S., giving the impression that there is something he does not want even his closest advisors to know; 4. It is presumed that investment in Donald Trump's properties have been used to "launder" money for Russian oligarchs, and only Donald Trump has refused to reveal his tax returns, the first POTUS in 50 years, in others: Donald Trump is being paid by Russians who are close to and often follow the dictates of Vladimir Putin; 5. Donald Trump has largely opposed strengthening the American electoral system against foreign, Russian, interference; 6. Donald Trump has attempted to prove that it was not Russia but some other nation that interfered in American elections, when all U.S. intelligence agencies unanimously testify it was Russia; 7. POTUS has taken Vladimir Putin's word over the testimony of American intelligence services;
Therefore, according to the philosophical reasoning of Occam's Razor, it is most likely that Donald Trump is, in fact, making decisions benefitting Russia rather than the U.S.