When Dwight Eisenhower and John Kennedy were in the White House, about 75 percent of Americans trusted the federal government to do the right thing most of the time. That number began to plummet during Lyndon Johnson’s administration and by Election Day 1968 had fallen to the low 60s. It continued to fall under Richard Nixon, and by the time Jimmy Carter’s term as president had ended, public trust in the federal government was down to just 30 percent. It briefly spiked above 50 percent after 9/11, then sank even lower. Barack Obama’s presidency saw public trust fall to the teens, which is where it remains under Donald Trump.

Why did Americans stop trusting their government? There is no single answer, of course. But perhaps part of the reason is that the size and scope of the federal establishment metastasized far beyond the level at which it could maintain a reputation for fairness and reliability. Since the 1960s and 1970s, Washington has insisted on doing more, regulating more, intervening more, spending more, and micromanaging more than ever before. As the view increasingly took hold that the government is obliged to solve every problem, its inevitable failure to do so became impossible to ignore. The bigger government grew and the more it intruded in citizens’ lives, the sourer the taste it left in many mouths.

Americans embark on this presidential election year with their trust in Washington’s abilities at or near an all-time low. Yet most of the Democratic politicians running for president want the government to be given even greater powers. As vast as the federal behemoth has grown, Elizabeth Warren, Bernie Sanders, Pete Buttigieg, and the others want it to grow vaster. In countless areas of life — medical costs, energy, college loans, gun control, labor unions, child care, and so many others — they call for more regulation, greater spending, new entitlements. They propose sweeping economic transformations and radical social shifts. And never do they voice even a qualm about the wisdom of conferring more authority and dominance on a bloated government that most Americans say they don’t trust.

The same politicians and political activists who mistrust so many people in the private sector feel no such wariness about the public sector. Everywhere they look, these politicians see citizens who cannot be trusted to make decisions for themselves: employers, gun owners, Big Tech executives, oil producers, health insurers, Wall Street investors, even Christian bakers and florists. Despite all the evidence to the contrary, however, they never seem to lose their faith — their almost religious faith — in the fundamental wisdom and benevolence of government regulators.

Atheists sometimes scorn religious believers as irrational for having faith in an omniscient God. But while God’s existence can be neither proved nor disproved, every day’s news brings fresh evidence of incompetence, fraud, waste, and dishonesty in government: Presidential impeachments. Police brutality. City Hall shakedowns. Campaign-finance chicanery. Men and women who work for the state may not be more prone to venality, bias, or screwing up than other people. But surely they are no less so.

Politicians and public officials are only human. They aren’t endowed with superhuman powers or godlike insights. They cannot foretell the future or avoid error. Their moral judgments are no better, on average, than those of the taxpayers who support them. And their schemes and projects are about as likely to succeed as most endeavors are.

An estimated 95 percent of product launches fizzle. Half of all new hires don’t work out. Twenty percent of small businesses go bust within a year. If the odds against success are so high even in such limited undertakings, how likely is it that the massive plans touted by candidates like Warren, who has issued more than 60 blueprints, many quite radical, for reconstructing American society, would work out as planned? Even if you find her (or any other candidate’s) ideas appealing in the abstract, isn’t it overwhelmingly likely that they would fail in the real world? And when that happened, wouldn’t the result be even more cynicism toward the federal government?

This month marks the 190th anniversary of an essay every candidate for office ought to read. In January 1830, the British historian and statesman Thomas Babington Macaulay wrote a review of a book on politics and history by Robert Southey, England’s poet laureate. Macaulay, a classical liberal, scathingly rejected Southey’s statist worldview:

“He conceives that the business of the magistrate is, not merely to see that the persons and property of the people are secure from attack, but that he ought to be a jack-of-all-trades, architect, engineer, schoolmaster, merchant, theologian … His principle is … that no man can do anything so well for himself as his rulers … can do it for him, and that a government approaches nearer and nearer to perfection, in proportion as it interferes more and more with the habits and notions of individuals.”

It may be appealing, wrote Macaulay, to imagine that a wise government should guide the people. “But is there any reason for believing that a government is more likely to lead the people in the right way than the people to fall into the right way of themselves?”

Macaulay’s plea for prudence and modesty in government is even more relevant in our time than it was in his — and even more likely to go unheeded. Never has America’s political class been so sure that it knows exactly how to engineer society. And never have Americans trusted their government less.

(Jeff Jacoby is a columnist for The Boston Globe).