Today, however, this problem-solving mentality is set against powerful currents in our political culture that portray government as corrupt and ineffective. The public sector’s reputation has crumbled, with trust in federal officials and in Congress — once relatively high — reaching record lows. According to the Pew Research Center, “Fewer than three in 10 Americans have expressed trust in government in every major national poll conducted since July 2007 — the longest period of low trust in government seen in more than 50 years.”

The fiercest attacks come from the right: In apocalyptic terms, conservatives attack government as an enemy — not an essential complement — of markets. Yet the left has its own sources of skepticism. Calling for a “political revolution,” Mr. Sanders casts government as so captured by powerful interests that only a popular upsurge will right the situation. This stance may not have the same anti-government tenor as conservatives’, but it sets up an impossibly high standard for reform and slights government’s continuing achievements (including the much-maligned Affordable Care Act, which has broadened coverage without driving up health prices).

We are trapped in a vicious cycle: Disillusionment encourages dysfunction, and dysfunction empowers those who spread further disillusionment and dysfunction.

Breaking out of this cycle is particularly hard for candidates for public office. Their primary imperative is to win an election, not change the conversation. A candidate who wants to buck the trend must be willing to take on more than just campaign opponents (and Mrs. Clinton will certainly face fierce attacks for proposing to raise taxes and create new programs in the general election). They must also overcome a juggernaut of organized anti-government forces: market-worshiping think tanks, right-wing media, a more staunchly conservative business leadership. In the face of a skeptical electorate, it’s a tough sell — even for Democrats.

The emergence of Donald J. Trump makes a serious national conversation about government’s role even more improbable. Mr. Trump is not as reflexively against government as, say, Ted Cruz, but he supports cuts in taxes, heavily skewed toward the wealthy, that can be financed only by huge budget cuts or staggeringly large deficits. More important, his chaotic policy pronouncements and equally chaotic character hardly lend themselves to a campaign focused on policy issues or principles of governance. He is a candidate whose claim to fame is his lack of association with (and stunning lack of preparation for) conventional governance.

Mrs. Clinton is heir to an enormously successful bipartisan governing tradition. Yet this tradition has been disowned by the Republican Party and has lost allure within a significant segment of the Democratic Party; it also runs sharply against the grain of current public sentiments about government and politicians. In this hostile environment, it should come as no surprise that Mrs. Clinton has proved reluctant to lead the charge for a more balanced discussion of government’s role.

Still, however understandable, this circumspection comes at considerable cost. Mrs. Clinton’s mixed-economy philosophy is what most clearly distinguishes her from both Mr. Sanders and Mr. Trump, and most clearly marks her as an heir to President Obama — who, notwithstanding conservative charges of socialism, has mostly sought to adapt and update existing policies to address pressing problems like global warming, unaffordable health insurance and uneven and poor school quality. Mrs. Clinton’s proposals not only have popular appeal, but they also could be financed with relatively modest tax increases (the bipartisan Tax Policy Center calculates that they will increase revenues by around $110 billion a year over the next decade, with almost all the increase borne by the richest households).