The Republicans have a different dynamic, while they're declining as a National Party (it took Hillary to only "win" by negative 3 million votes), they have a core of support in about 15 states that's almost irreversible for the next 10-15 years:
Utah, Wyoming, ND, SD, Nebraska, Kansas, Oklahoma, Arkansas, LA, Miss, Ala, SC, Tenn, Ky, Indiana - the white states without major cities.
The rest of their support are the rural areas of traditionally conservative states that are going purple or even blue due to urban growth:
AZ, Texas, Montana, Florida, Georgia, NC, VA
and the rural areas of rustbelt states that wil swing back to the Democrats:
Minn, Iowa, Mi, Ohio, PA
So while this Presidential election was an anomaly (the Democrats will start 2020 with a 5-7+M plus advantage nationally, Demographics are on their side), control of Congress is tougher, the Democrats have to elect senators from purple states.
One factor that's not talked about is the shift of votes from the North to South and Southwest, this actually hurts the Republicans, because a lot of the migrants are younger people moving from Republican northern areas to Southern Urban areas - the core Republican rural areas are depopulating both due to outmigration and death (when your base of support is over 40 white people, it has a tendency to literally die off). The next realignment in the 2020s will shift more northern votes to urban and suburban areas - you can only gerrymander so much - and in the South, the same trend as cities continue to grow. You can see this impact in Virginia and North Carolina, NC was a staunchly conservative state a couple decades ago.
But while the Tea Party could spend last decade moving moderately conservative areas further right - in effect, ignoring the center by strengthening control over "cows" - House districts which were safe from Democrats, that strategy won't work for the Democrats. Note the Tea Party's power was their influence over Republicans, Obama's problem was the Democrats simply don't vote.
For the Democrats to regain power, they have to take all the moderale and slightly conservative districts that come up for grabs due to demographics - the Democratic core is too small to control either house, 5 NE states, NY, NJ, Del, MD, CA, Ore, Wash, NV, NM, HI - that's only 30 Senators. You have to take back most of the rust belt states, and turn, Texas, Florida, NC, Maine, NH, etc. It's not enough to win the popular vote in the Presidential race, you have to win governships and suburban house races.
That means they can't use Tea Party tactics, because only 20% of America is leftist, you have to placate the 45% in the center to become the majority party.
Which means tactics build around identify politics, anti-business rhetoric, protests, etc. are not going to work.
The Democrats have to tone down the rhetoric, push the idea that progress is gradual and requres both long-term commitment and compromise.
Spend less money organizating protests and more money financing whatever it takes to register voters and get them to the polls in the off-years.
Fortunately, Trump is the greatest argument for that approach - and by simply contrasting Obama and Trump, the Democrats can win that argument.