The truth is that I have had the same model in my mind for 25 years of where American national politics should be headed, a realignment that would allow us finally to get past the 50-50 partisan deadlock which our current format will not permit us to break. Frankly, I'm surprised it hasn't happened yet, but maybe saying it out loud will make it happen now--the conditions seem ripe to me.
First, the endpoint: a 3-party system with, let's call them: The Constitutionalists (Tea Party, Libertarians, and Isolationists), the non-ideological Middle Party (Blue Dog DINO's, moderate Republicans, Trumpocrats, and Trilateralists), and the Real Democrats (Sanders/Warren wing Progressives). That Middle Party might be the natural party of governance, but they would need the assistance of the Real Democrats or the Constitutionalists for certain purposes.
To get there, the first essential step is the weakening of the Republican party: they are taking care of that themselves (with the help of the interloper Trump). Hillary Clinton gets it started with a solid Electoral College win in 2016 and brings with her a small Senate majority, reducing the Republicans majority in the House. A good term for Hillary (despite losing control of the senate in 2018), she announces she's sick of it all and endorses a promising young (but not too young) successor, and the Democrats smash the Republicans' stranglehold on the statehouses in 2020, setting up a turnover of control in the House (after redistricting). Then the Democrats can start to cannibalize themselves, which would be the logical next step--it probably wouldn't take more than 6-8 years, so the evolution could be complete by 2028.
I actually think such a setup would make most everyone happier: purists like me and the Constitutionalists would have parties they could wholeheartedly support (I would be happy among the Real Democrats, for most elections). They would not be irrelevant; while the moderates, who are also very dissatisfied with the partisan polarization, would be much happier and could get down to BAU.
The first steps, for 2016, are not really that challenging, assuming Her Royal Clintonness is up to the task. In the Senate, the Republicans have to play defense; the Democrats have to gain a net of four seats (with Democrats remaining in the White House, and their VP presiding in the Senate as needed), and there are plenty of opportunities. The best two are in Wisconsin, with Russ Feingold favored to win back his seat, and in Illinois, where the Democratic majority should prevail--with war hero Tammy Duckworth--over the slippery Mark Kirk. Next is Florida, assuming Marco Rubio does not bail on his Presidential campaign and to run for re-election, and there are good opportunities in Ohio, New Hampshire, and Pennsylvania. The trick, for the Democrats, will be that they cannot afford any slippage, so the races in Nevada, in which Harry Reid will be stepping aside, and Colorado will be critical to hold. Then there is the need to avoid a political fiasco in North Dakota, a Democratic seat which Heidi Heitkamp won somewhat flukily in 2012; she will be tempted to abandon her seat rather than lose it in 2018 and run for something else, like governor, which would make the seat a likely Republican pick-up in a special election.
With regard to the House, the cards are stacked against the Democrats; even with a wave election, which I do believe is possible, probably they could gain 20 seats or so and make it close, which would be useful for some legislative tasks. The big realignment would have to wait for another favorable outcome in 2020 (4 Presidential elections in a row for the Democrats would surely be definitive for a break-up of the national Republicans), and some heavy-handed maneuvering in the states. In the meantime, some tough Senate seats won by the Democrats in 2012 will be highly vulnerable in 2018 should the GOP get it together for a last-chance power drive.