If 2016 was a bad year for to be a liberal, then 2017 burnishes that. There have been five special elections for vacated seats in congress, and all five were retained by the GOP. The Democratic Party tried four completely different strategies in all four races, and despite a relatively narrow loss for Jon Ossoff in Georgia, they were all abject failures.
Unfortunately, the Democratic Party as it stands now is aging and out of touch. The 2014 midterms and the 2016 election both exposed the lack of bench depth. President Obama is retired more or less, and party luminaries like Sec. Hillary Clinton, Charles Schumer, Nancy Pelosi, Elizabeth Warren, Bernie Sanders, and Dick Durbin are all on the wrong side of 65. It is a party whose platform should appeal to millennials, a group that is more keen on social issues than any other generation in American history, and the Democrats are muffing it.
Even though we still have plenty of time to speculate, the field of candidates in 2020 so far isn't offering much promise. Martin O'Malley, the man who finished a distant third in the 2016 primaries, is not only perceived as too moderate, but has a history of race issues. Corey Booker has foot-in-mouth disease and too many corporate ties. Warren might be the most suitable, if she's willing to run, but she'll also be 71 years old on Election Day. Barring some minor miracle, we could very well be stuck with President Trump until 2025, when he'll be 78 and even more unintelligible than he is now.