But in a polarized polity, can public opinion ever check presidential power? Our research suggests that it can. But Congress has an important role in jump-starting this popular constraint.

Right now, institutional checks are weak

The opening weeks of the Trump administration have brought a flurry of executive actions on issues including the temporary ban on entry into the United States for citizens of seven majority-Muslim countries, the border wall and the long-stalled Keystone XL Pipeline.

But while President Trump’s actions have provoked an unusual level of criticism, a president’s quick use of unilateral power is hardly new.

Candidate Barack Obama critiqued what he called excessive unilateralism by President George W. Bush. But when blocked legislatively, Obama acted unilaterally to tweak implementation of the Affordable Care Act, regulate greenhouse gas emissions and shield millions of undocumented immigrants from deportation.

Historically, many executive actions have prompted considerable outcry in Congress. But in case after case, Congress has been all bark and no bite.

While court rulings can’t be vetoed, they depend on the executive to be enforced. As a result, strategic courts rarely overturn executive actions.

In short, the system of checks and balances on executive action appears to be broken. Critics charge that the limits on executive power have given way to an imperial presidency.

But public opinion can be a bulwark against creeping executive power.

When contemplating executive action, presidents — at least, past presidents — have not only considered the (usually very small) chance of Congress or the courts overturning their initiatives, but also any action’s potential political costs.

Perhaps above all, presidents consider the likely public reaction. Popular support is essential to presidents’ political capital in Washington, allowing them to get more of what they want from Congress, and shaping their own and their party’s electoral fortunes.

What do Americans think about unilateral action? In the abstract, many Americans say they are deeply skeptical of it, seeing it as an affront to separation of powers.

And yet, when assessing major actions by presidents Bush and Obama, public opinion divides predictably along partisan and policy lines. Most Americans support executive actions by a president of “their” party or that moves policy in their preferred direction, while they oppose actions by the “other” side that go the “wrong” way, in their view.

Does Congress lead or follow public opinion?

In the summer of 2014, House Speaker John A. Boehner publicly critiqued Obama’s increasingly unilateral approach, saying:

The current president believes he has the power to make his own laws — at times even boasting about it. … The House has an obligation to stand up for the Legislative Branch, and the Constitution, and that is exactly what we will do.

Predictably, Boehner’s Congress did not produce a single bill to overturn an executive action.

Such verbal displays are often dismissed as empty rhetoric — good political theater, but of little consequence.

But it’s not so. To be sure, congressional broadsides result in more media coverage than concrete legislative action. But high-profile criticism may influence public opinion — and that has power.

Determining whether congressional rhetoric drives public opinion is difficult. If we see members of Congress challenging presidential orders that prove unpopular, it’s hard to tell whether congressional opposition reduced public support — or whether public disapproval pushed congressional critics to speak out, pandering to mass opinion.

Here’s how we did our research

To figure out whether Congress can move opinion, we conducted randomized experiments embedded in national opinion surveys. One of these explored public support for one of Obama’s most important and polarizing executive actions: the Clean Power Plan.

All survey respondents were told that Obama had ordered the Environmental Protection Agency to begin regulating carbon dioxide emissions to protect public health and combat climate change. Subjects in the baseline control group received no further information. Other subjects were assigned to one of two groups and were told that members of Congress had criticized the plan. Half of these were told the criticism came from congressional Democrats; the other half, from congressional Republicans.

Even on a politically fraught issue, congressional criticism significantly eroded support for Obama’s action, as you can see in the figure below. The effect was biggest when the president’s fellow Democrats challenged the action, leading to a 17 percent drop in support. But even criticism from opposition Republicans lowered support by a significant 14 percent.

We did similar experiments on a variety of domestic and foreign policy issues. All these confirmed that members of Congress can reduce Americans’ support for unilateral executive actions.

The temporary ban on citizens of seven majority-Muslim nations kicked up a lot of criticism 

Trump’s executive order temporarily banning citizens of seven majority-Muslim countries from entering the United States triggered widespread criticism from Capitol Hill, even from many prominent Republicans. Our results suggest that this reaction may have increased public opposition to the order.

Moreover, this congressional and public backlash may have contributed to the administration’s recent defeats in the courtroom. While judges rarely challenge executive actions, research suggests that judges are more likely to rebuke unilateral presidential actions when they know Congress and the public agree that the president went too far.

Congressional criticism, in other words, may have emboldened the courts to formally check the president.

Congress’s objections are more powerful than they seem

Congress may have more power to hold back a unilateral executive than commonly thought. Even when it can’t overturn an executive action through law, congressional opponents can mobilize public opinion against the president — and sometimes, presidents reverse themselves as a result.

Perhaps more important, most presidents seem to think about the potential costs they’d face if they go too far and provoke congressional pushback. Presidents who think the cost is too high might forgo unilateral action altogether.

Whether Trump expected (or cared about) such opposition is anybody’s guess. But he has already paid a price for missing this history lesson. 

Douglas L. Kriner is an associate professor of political science at Boston University.

Dino P. Christenson is an associate professor of political science at Boston University.