Hillary Clinton’s move to the left on trade and other issues is a reminder of the growing power of activists in the wings in presidential nominating politics — and a corresponding diminution of the power of the center.

“Social and demographic shifts mean that no left-leaning position Clinton takes now would be likely to hurt her” in next year’s general election, The Post’s Anne Gearan writes in a recent assessment of Clinton’s strategy. Meanwhile, GOP candidates are doubling down in the other direction, as they move toward their party’s right wing.

The disenfranchisement of the center is a fact of modern politics. That should be worrisome even if you think the center is an ideological muddle. As we’ve seen in recent years, in a world dominated by the political wings, the compromises necessary for passing any legislation become difficult. As the center disappears, so does governance.

To illustrate how the current system works, a would-be reformer named Peter Ackerman recently showed me a diagram that estimates party affiliation: “Democrats: Less than 30 percent,” “Republicans: Less than 30 percent,” and in the middle, “Unaffiliated: Greater than 40 percent.” He argues that if you include left-leaning and right-leaning voters in the “moderate” camp, they make up two-thirds of the electorate.

Yet as we head toward the presidential nominating season, the voice of this broad center is barely audible. Politics is pulled toward the left and right by campaign-finance rules, redistricting and other issues discussed in countless essays and op-eds. This centrifugal force seems to increase in every election cycle, with a resulting paralysis in Washington.

Ackerman has launched a campaign dubbed Change the Rule to address one piece of this puzzle of American political dysfunction. The rule in question is imposed by the Commission on Presidential Debates, which the two major parties created in 1987 to administer the televised debates that are the nexus of modern presidential campaigns. Ackerman argues that this rule, as currently applied, prevents the emergence of an independent candidate who might empower the underrepresented middle.

The debate rule requires that any third-party candidate must average 15 percent support in five polls taken in the two weeks before the debates begin in October of the election year. To get the necessary name recognition and support, Ackerman’s group estimates that an independent candidate would have to spend $266 million. Because of contribution limits, this effectively precludes anyone who’s not a billionaire.

Ackerman argues that the entry ticket to the debate should instead be getting on the ballots by the end of April of an election year in states that together have at least 270 electoral college votes. To avoid chaotic debates, just one such independent candidate should be added — the one with the highest number of ballot-access signatures nationwide. Such a signature drive would cost less than $15 million, Ackerman estimates, opening the field to less wealthy candidates who could mobilize volunteers and small donations.

Supporters are a “who’s who” of the bipartisan center: John Anderson, a Republican and former congressman who ran as an independent in the 1980 presidential race; William Cohen, a Republican and former senator who served as defense secretary for a Democratic president; Lee Hamilton, a Democrat and former congressman who co-chaired bipartisan commissions on 9/11 and the Iraq war; Jon Huntsman, a Republican and former governor whose moderate positions vaporized his 2012 presidential campaign; and Joe Lieberman, a Democrat and former senator and vice presidential nominee. Other backers include retired Gen. Stanley McChrystal and retired Adm. James Stavridis.

To bolster the case, Ackerman commissioned a survey in July by pollster Douglas Schoen. In the sample of 1,000 likely voters, 86 percent said that the political system is broken and doesn’t serve ordinary people; 89 percent said that they wished politicians would work together and compromise; and, interestingly, 66 percent said that they thought presidential debates could do a better job of informing the electorate.

Other surveys reflect this deep mistrust of the system. A Pew Research Center poll conducted in January reported a 48 percent unfavorability rating for the Democratic Party and a 53 percent negative one for the Republicans. A Gallup survey in August found that 83 percent disapproved of the job Congress is doing.

Yet the system grinds forward with a perverse set of incentives that reward extremism and punish compromise. I don’t know whether opening the presidential debates would fix this mess, but it might pull candidates back toward the center, where the public lives and where problems get solved.

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