No liberal has claimed that Russia forced people to vote for Trump. What they claim, because it is true, is that Russia ran an extensive multimillion dollar covert influence campaign aimed at hurting Clinton and boosting Trump. Some of this involved social media ads which reached tens of millions of American voters. The more spectacular part is the theft and strategic release of emails from Democratic sources. The Russians used these emails to disrupt the Democratic campaign and help Trump. For instance, the first batch of emails were released on the eve of the Democratic National Convention, when Clinton was trying to unite Democrats after a hard fought primary. Other batches were released throughout the campaign, timed to aid Trump or hurt Clinton. For example, just thirty minutes after the Washington Post published a story detailing how Trump bragged on tape about sexually assaulting women, the Russians, through wikileaks, released more emails. This helped muddy the news cycle about the tape, particularly in conservative circles, as well as helping to distract from the US Governments announcement earlier in the day that the Russians were behind the hacks.
The idea that these could have influence voters isn't idiotic. Remember, Republicans insist that bias in the news media is mostly responsible for Democratic electoral successes. I've seen numerous Republicans claim that without such bias, and the favorable news coverage which results from it, Barack Obama would never have been elected and Democrats would rarely, if ever, win elections. If all that's possible from bias in the news media then it's certainly possible that a multi million dollar influence campaign by a foreign government could have swayed some voters, perhaps even the couple thousand voters who gave Trump his margin of victory in key Rust Belt states.