There are two ways to lie in politics. Let’s say Side A wants to spend more on government, and Side B wants to spend less. Side A might exaggerate the benefits of investing in poor communities, and Side B might tell a story about how tax cuts for the rich will pay for themselves. This can be called directional lying, with each side trying to convince you of something, and this is how politics pretty much worked until the last few years.
Republicans, because they are tribal and not ideological, do not punish their politicians for non-directional lying, or simply making things up. I already mentioned the schizophrenic messaging about Biden and crime.
Trump mostly governed like a typical Republican, and his administration pushed for things like less spending on entitlements. Republicans meanwhile have been running ads accusing Democrats of wanting to cut Medicare. The party made opposition to Obamacare maybe its central political messages across three election cycles. Before his 2018 Senate election, Josh Hawley had signed his name to a complaint that would have gotten the Supreme Court to overturn Obamacare. He also ran an ad saying he wanted to protect people with preexisting conditions from losing their health insurance. You can be generous to Hawley and assume that maybe he liked the preexisting conditions part of Obamacare, but thought the law was so bad overall it still needed to go. Still, the practical effect of voting for Hawley and other Republicans in that election was that they would make it less likely insurance companies would have to cover preexisting conditions, making this a case of non-directional lying.
Trump supporters argued he was the most pro-gay rights presidential candidate in history. Meanwhile, his administration rolled back anti-discrimination protections. You can say that “gay rights” is not synonymous with “the policy wishes of the LGBT activist community,” but that’s how most people understand these terms. Anti-discrimination laws based on sexual orientation and gender identity have wide popular support, meaning that when most people hear a politician saying he is pro-gay rights, they assume he supports such policies. And maybe Trump actually does, but in his administration it was social conservatives who set the agenda.
Liberals say really false things like “men can get pregnant,” “police are killing large numbers of innocent black men,” and “poor people are more likely to be fat because of food deserts.” Yet these are lies (or more usually, kinds of self-delusion) that you would expect from people who’ve adopted crazy ideological commitments: the blank slate theory of human nature, an aversion towards “blaming the victim,” championing minority sexual identities as normative ideals, and a worldview where the problems of the poor can always be blamed on their oppressors. Russiagate was a kind of paranoia of the left that was similar to the conspiracy theories of the right.