Only won the popular vote once since 1988.
Lost their House majority.
Has effectively become a personality cult built around one individual who will very likely be dead or in jail within the next few years.
Has shown no ability to get their base out to vote when said individual is not on the ballot.
Has plummeted with white, college-educated and suburban voters (the highest propensity voters).
Electoral college and Senate advantages may be slipping as states like AZ, GA, NC, TX move left.
Base is dying off, party has almost zero appeal to future generations and growing demographics.
Literally doesn't even have a platform anymore.
If we're going to ask this question about the Democratic Party, which just won the presidency against an incumbent who couldn't even get 47% of the vote, why not ask it about a party that you could make a much better case is slowly but surely declining?
Neither party is going anywhere and presidential elections will be hard-fought tossups well into the future. The Democrats are at a serious disadvantage in the Electoral College though which makes it easier for Republicans to win while losing the popular vote and this scenario will likely happen again in the next 20 years. Republicans also need to do better among younger voters in future elections although most people do tend to get more conservative as they age.