For those who don't recall, Russia had big reasons to endorse Trump over Hillary in 2016: Hillary was bellicose about Russia and Syria, to the point where people echoed worries she'd plunge us into "WW3". That, compared with Trump's contrarian sympathies toward Russia and irreverence about the U.S.'s moral highground (and conservatism AND clear, probable incompetence) of course motivated Russia to support him.

They also hoped that he would come to the table and legitimize Russia as a fellow superpower and usher in a new era of diplomatic relations. The fact that Trump utterly failed to do that probably chilled Russia's interest in the 2020 election though.

Read more here: https://www.bbc.com/news/election-us-2020-53702872