Whoever wins the nominations, the most successful campaigns of 2016 provide us with a clear picture of where the center of gravity is today in both parties and, hence, where America is going.
Bernie Sanders, with his mammoth crowds and mass support among the young, represents, as did George McGovern in 1972, despite his defeat, the future of the Democratic Party.
That Hillary Clinton has been tacking left tells you Sanders is winning the argument. Should she avoid indictment in the email scandal, and win the nomination and the election, Clinton would be a placeholder president.
Yet, should Sanders win the nomination and election -- highly improbable -- he would become a frustrated and a failed president.
Why? Consider what he has on offer.
Free college tuition and universal health care, a breakup of the big banks and a reform of the tax code to make the Fortune 500 and the millionaires and billionaires pay for it all. Soak the rich!
Sound socialist economics, but this is the formula that turned Puerto Rico and Illinois into the booming showcases they are today. Moreover, unless Sanders swept both houses of Congress and won a 67-vote, veto-proof majority in the Senate, his agenda would be dead on arrival on Capitol Hill.
Yet there are areas where the Sanders agenda overlaps that of Donald Trump and other Republican candidates. Bernie is an anti-interventionist, anti-nation-building, anti-empire leftist of a breed common in the Labor Party after World War II, when the British Empire was liquidated, Churchill notwithstanding.
Moreover, Sanders is no free-trade globalist of the Davos school. He opposed NAFTA, GATT and MFN for China. Like Trump, he backs a trade policy that puts American workers first.
Thus, on both trade and foreign policy, there is common ground between the rebellions in the Democratic and Republican parties, even as Clinton has ideological allies among the GOP free-traders and neocons of the Bush I and II presidencies.
But while difficult to see how Sanders captures the nomination and wins in November, the rebellion in the GOP is larger, stronger and deeper. In every national or state poll, anti-establishment candidates command a majority of Republican voters. Which presents a problem for the establishment.
The Beltway elites may succeed in blocking Trump or Ted Cruz. But the eventual nominee and the party will have to respect and to some degree accommodate the agendas of the rebellion on immigration, border security, trade and anti-intervention, or face a fatal split.
We have been here before.
After Richard Nixon lost to JFK in 1960, the Goldwater movement arose to capture the party. While it went down to a legendary defeat, those who wrote off 1964 as the temporary insanity of the radical right, and walked away from the nominee, were the ones who were history.
Nixon incorporated the conservative movement into his New Majority. Ronald Reagan reveled in the Goldwater title of Mr. Conservative and welcomed into the party the rising Moral Majority.
But it was the dismissive stance of Bush I toward the populist revolt in his party, and his indifference to concerns about illegal immigration, border security and the export of U.S. factories and jobs that brought Ross Perot into the '92 race, and cost Bush his second term.
Today, the Republican leadership faces another insurrection. Either it will find a way to accommodate this rebellion, which is not going away after 2016, or it will find itself suffering the fate of the Rockefellers and Romneys, the establishment leaders of the 1960s.
While Sanders is an ideologue who has been on the far left of the political spectrum all his life, instinct, more than ideology, explains Trump. His success comes of having seen, felt and given voice to the broad anger of Middle America.
The old GOP agenda -- roll back the Great Society, reduce the size of government, cut capital gains taxes, reduce marginal tax rates, balance the budget -- this is not the red meat of the Trump rallies.
Populism, patriotism, nationalism, defying political correctness and dissing the establishment and the elites that monitor PC are where it's at. And there are reasons for such populist rage.
Put bluntly, the nation seems almost everywhere on an unsustainable path. Mass immigration, legal and illegal, continues to alter the face of America. Obama doubled the debt, and the deficits are rising again.
Abroad, we are apparently going to keep troops in Afghanistan for generations, send more to Iraq and Syria, bring down Assad but keep ISIS and al-Qaida out of Damascus, confront Beijing over the Spratley and Paracel Islands in the South China Sea, build up U.S. forces in the Baltic states and Poland, send weapons to Ukraine, sanction Vladimir Putin for Crimea, repudiate the Iran nuclear deal and reimpose sanctions -- all to be done while our NATO, Arab and Asian allies helpfully hold our coat.
The next president, be it Trump, Cruz, Clinton or Sanders, either will be the last president of an old era, or the first president of a new era.