This is largely untrue and there are stark differences between Democrats’ complaints about the 2016 election and the Republicans’ claims about the 2020 election.
Democrats felt that there was a concerted effort by foreign countries (primarily Russia) to influence the outcome of the election. They did this by using social media accounts to spread misinformation and outright falsehoods to the public in a systematic effort to confuse voters and sew division in the electorate. This proved out to be true, and I’m sure its something they’re still doing.
There were concerns over whether or not they could/did access voter rolls and whether they could actually impact someone’s voter registration or actually change votes and there was no evidence that they did this. While I’m sure there were some leftists who claimed actual election fraud, most mainstream Democrats accepted that there wasn’t really any controversy in the actual counting of the votes, but rather a larger systemic problem of massive amounts of misinformation being distributed to voters by foreign governments and domestic ”news” outlets.
Of course then the concern became whether or not the Trump campaign had actively worked with Russian officials in their efforts to have him elected and in particular there was concern as to whether Russian officials had shared intelligence on political opponents to the Trump campaign or vice versa. As It turned out, there were in fact some members of the Trump campaign and administration who were guilty of this and several people were indicted, though it was concluded that the President himself was likely not directly involved.
The Republican claims over voter fraud in 2020, like any voter fraud claims in 2016, were completely baseless and void of any evidence. There was another massive misinformation campaign to spread lies about fraudulent election practices. They were so baseless that every single challenge in court was thrown out, including by the Supreme Court which contains 3 Trump appointed justices. Here in Texas, the only actually documented case of voter fraud was committed by Republicans in a local election.
These baseless claims were accepted and spread by mainstream Republican politicians, including the President. This led to unprecedented challenges to the vote which undermined the integrity of American elections - which seems to have been a key goal of the Russian interference that took place in 2016. The mainstream Republicans lending credibility to these outlandish claims eventually lead to an attempted coup on our nation’s capitol, where those who believed that the election was being stolen stormed into the capitol, killed a capitol police officer, and attempted to access the house chamber where representatives were. They came so close to making it into the congressional chamber that one person was shot and killed in their attempt at sedition.
Still, Republicans continue to feed into conspiracy theories and are now actively trying to change election laws to make it more difficult for people who likely would not vote for them to vote at all and to give power to state legislatures to overturn election results that they do not like.
So, in sum...the election issues that were brought up in 2016 turned out to be legtitimate. A foreign government DID attempt to systematically influence the election and some campaign officials DID break the law by colluding with them. The election issues brought up in 2020 were completely baseless but lead to a treasonous riot at the capitol building and is eroding American democracy and leading us closer and closer to the Fascism that President Trump so wished for.