The two parties have never been singular ideologically cohesive organizations, but a coalition of various governing philosophes and special interests.  In parliamentary governments with numerous parties that each gain proportional representation at election time, such coalition governments are formed after the election.  In our two-party system this coalition forms beforehand.

This is the reason third parties have had such a difficult time in the United States.  Generally, they form around either a single issue or reflect a particular passion, but they lack a willing partner to form a successful coalition.  For example, Reagan was elected largely by a coalition of the pro-lifers energized by the recent Roe v. Wade decision and the supply-side tax-cutters represented by Arthur Laffer.

The Republicans are a coalition of Main Street Capitalists, Christian Fundamentalists, Populists, Constitutional Conservatives, and the Leviathans.  The last group represents large government and could be considered Hamiltonian Federalists by us history geeks, but that would only alienate us more from the Populist movement.

The critical issues for the current GOP coalition are Second Amendment rights, wage stagnation, security, the pro-life movement, and immigration.  This last issue is burning particularly hot this cycle, but in many minds, it is tied to wage stagnation and security.

The Democrats are a coalition of Progressivists, Socialists, Populists, Mercantilists (some may substitute Crony Capitalists), and Unions.  Their critical issues are abortion rights, environmentalism, gay and minority rights, and economic inequality.

Republican populists warn of the demons of big government; Democratic populists warn of the demons of the One Percent.  I would not be surprised to see many of the populists who supported Bernie become supporters of Trump.  Their demons are increasingly interchangeable.  Demons are critical to populist movements, and movements based on demons need saviors.

For the Republicans, the Constitution's mission is to protect the individuals from the intrusion on their natural rights from any concentration of power in the federal government.  For the Democrats, government should protect individual rights from the concentrated economic power in the private sector, and constitutional restrictions on government power are an impediment to their mission.

The Trump phenomenon has witnessed a major shift in the GOP away from the Constitutional Conservatives and Leviathans.  Trump has extended the appeal of the Tea Party and continued to bring new voters out, even if the motivating force is one of frustration rather than clear governing principles.  These new voters have changed the dynamics of the Republican governing coalitions.  There is a weaker demand for the kind of government experience of a Jeb Bush or a John Kasich or the clear constitutional and conservative principles of a Ben Sasse.  

There remains, however, a hunger for a leader who can connect these important intellectual principles with the real concerns of voters.  While the Democrats may remain intellectually vacuous, the old GOP remains politically tone-deaf.  Litmus-test Republicans who were accepted in their big tent as long as they were controlled are now in control, or close enough to cause the old coalition to convulse.  Perhaps the Republican tent was a little too big and inviting for the new Trump voters.

Remember how concerned the GOP was with Trump mounting a third-party campaign?  It is quite unexpected that Trump would become so successful that he would need to expend effort to fight a third-party effort from the establishment.

The Democrats have maintained their controlling coalition in spite of Bernie Sanders's challenge because the difference between the dominant progressivism and the challenging socialism is only one of degrees.  Both Debbie Wasserman Schultz and Hillary Clinton were unable to articulate the difference when asked by Chris Matthews.

The appearance that the parties have become less relevant is just the loud shifting of coalitions.  Party politics remain too powerful, and the Constitution is designed to limit rapid and radical change.

If Hillary wins the White House she will have the compliance of her party and, depending on how successful the Republicans are in maintaining their majorities, will be less restrained.  Trump will face not only a terrified Democrat opposition, but the old Republican coalition that will still dominate the Congress. 

Economist Don Boudreaux noted that Hillary is more likely to get the benefit of the doubt from the Congress and the media; Trump will get no benefit of the doubt from anyone.  Neither one of them deserves it. 

This will be a fascinating campaign to unfold.  It was foreseen by Angelo Codevilla in his important article in The American Spectator six years ago, "America's Ruling Class and the Perils of Revolution."  While I and many others grossly underestimated the force behind the Trump rise, it does seem that this middle-class revolution will not be ignored.  The Democrats would be foolish to consider this merely a Republican problem.