Simple. Trump had been working on a deal with Russia to build a multi-million dollar hotel in Russia, which would have been the tallest building in Moscow, and right across the street from the Kremlin. The project was first brought up in 2005, and the Trump organization sent Russia a letter of intent in Jan. of 2016. When Russia failed to respond in a timely manner, Trump pulled out of the deal.
It stands to reason that there would be plenty of contact between the Trump organization and Russia over those 10+ years, but naturally, desperate libs like you will nevertheless bend over backwards trying to find something criminal about it.