Remember when the grown-ups in congress were going to check the worst impulses of the president? That was the rationalization offered to reluctant Republicans by those trying to unify the party around a presidential candidate with authoritarian tendencies. Sure, he’s reckless and crazy, but Trump will be kept in line by the adults in the legislative branch.

In fact, there have been external checks on the president during these dizzying first four months of the Trump administration, but congress has not been among them. We have seen pushback from corners of the judiciary and the permanent bureaucracy, from some journalists and opinion leaders and most importantly from the energized crowds that took to the streets on day two of the administration and continue to disrupt congressional constituent meetings with vocal, pointed opposition. But from congressional Republicans there is mostly silence, punctuated occasionally by expressions of concern about the president’s anti-democratic behavior but, thus far, no substantive action.

There is a good reason for this, and you need look no further than today’s Gallup Poll to find it. Solid majorities have disapproved of Trump’s performance in office almost every day since the first week of his presidency. His overall job approval hovers around 40%, a record-shattering low for a new president. But Republicans inhabit a different world, where Trump’s performance gets a thumbs-up from 84% of his fellow partisans. Congressional Republicans, especially those representing gerrymandered districts, cross these voters at their own risk.

The practical effect of this skew in public opinion has been to create something akin to parliamentary governance, where the shared partisan interests of the president and congress override institutional differences and the checks and balances they are designed to create. This is why Republicans have been reluctant to call for an independent probe of Trump’s Russian connections even after he all but admitted he attempted to obstruct the FBI investigation this week by firing James Comey. Any action that might undermine the Trump administration would also undermine the Republican Party, as the fate of both will be determined by that sizable minority of voters who are out of step with the rest of the country. This leaves Republicans little choice. Absent the courage to put their party and careers on the line, they have to enable the erratic and dangerous behavior of their leader.

But other forces are squeezing congressional Republicans from outside their party base. As Trump’s behavior becomes more difficult to excuse, and as resistance from an angry public leads the vast majority of Republicans to avoid facing their constituents, the political costs of inaction begin to add up. Dick Durbin, the second-ranking Senate Democrat, told ABC News that “quietly, privately” Republicans have been “expressing their concerns” about the administration. Translation: they know that the longer they defend the loose cannon in the White House, the more he will define them. Enabling this president means melding the congressional party with someone who each day presents himself as a threat to the republic and the world, someone who has sparked a resistance movement and who is opposed by more than half the country. When this moment is over, Republicans will be called to account for their actions, for whether they succumbed to short-term political expediency or put the republic ahead of party, power and position.

There have been no profiles in courage so far, and with the next general election almost two full baseball seasons away, political calculations still favor enabling. But at some point that may change. Tomorrow, I leave for Washington with the Villanova program I run every spring. It will be interesting to see whether Republicans are reacting more strongly to the existential threats posed by the Trump administration to the country or to their party. I will report back what I learn.