In 2008, one of the first things that Obama had to do was staunch the bleeding from the housing collapse. This meant that a huge amount of capital needed to be expended on putting out the fire, and while that was happening, it gave the GOP an opportunity to regroup and aim for the mid-terms. The GOP in 2008 had also been pretty effective at severing their ties with the Bush White House while still retaining most of their base.
2016, the base is shattered. Trump has created a major divide between the Brand GOP loyalists and the hard right, and he, or someone like Breitbart, is going to use this to create the Patriot Party (or something similarly idiotic). This is going to create a de facto three party election in 2018, favoring the Democrats. I'm guessing that in addition to this, the GOP is going to have to start laying the groundwork to retain their electoral advantage in 2020 at the state level (in order to preserve their gerrymandered advantages), so they're going to be strapped for cash for 2018. This means pretty much ceding the mid-terms, and the Dem coffers are pretty much flush this year.
So there will be at least one election cycle past this one where the Dems have enough of a margin to really affect things at the Federal level. 2020 becomes the major test - candidate at the four-year point, a mild recession in the rear view window, so likely much of the divisiveness of 2016 will be past us. Progressives should be pretty content at that point, but Dems need to start laying the ground game at the state level in 2018 as well. Demographics favor them, but the Dems have to take back the governorships and state legislatures by 2020 as well.