Senator Bob Corker (R-Tenn.) speaks during a news conference on Capitol Hill in September. (EPA-EFE/REX/Shutterstock)

Last week began with a bang: Sen. Bob Corker (R-Tenn.), chairman of the Senate Foreign Relations Committee and a leading GOP voice on foreign policy, made startling comments disparaging President Trump, particularly his handling of foreign policy. Midweek, the world awaited Trump’s decision about the Iran nuclear deal. Even some who had opposed the Iran deal in 2015 called for staying in.

The week ended with Trump’s announcement that, rather than scrapping the deal, he would press Congress to amend the legislation associated with the deal to address what he called its “many serious flaws.”  As a coda, at the end of the week Corker renewed his public complaints about Trump’s undercutting of Secretary of State Rex Tillerson.

What does all this mean about the politics of foreign policy, nearly a year after Trump’s election? Here are four takeaways from last week’s events.

1. Corker’s comments may have opened a door.

Start with Corker. After his highly unusual comments about what he regards as Trump’s incompetence, some observers argued we may soon see more public GOP criticism of Trump. As Jonathan Bernstein points out, such direct criticism is unrealistic.

But Corker’s comments can still matter in less visible ways, particularly on foreign policy. Scholars of Congress and foreign policy have long noted that Congress constrains the president in more ways than may be obvious. For instance, when formulating policy, presidents have to anticipate how Congress will react.

Comments from someone like Corker — a GOP foreign policy leader at least until he retires — may give cover to other Republicans who want to differ with Trump. We saw some of that last week, when some congressional Republicans urged Trump not to scrap the Iran deal.

Even such comparatively mild intraparty criticism of the president matters. As Matthew Baum and Tim Groeling have shown, such signals are likely to be reported by the news media, and are surprising and informative to voters. There is also intraparty signaling within Congress, where those who are less informed on foreign policy are watching those with greater experience.

Corker’s comments made room for a wider range of GOP reaction not just on the Iran deal but on Trump’s future foreign policy moves.

2. Trump is also constrained within his own administration.

Reports suggest that many top Trump advisers also advocated staying in the Iran deal, and tried to get Trump to kick action to Congress so he could decertify without blowing up the agreement.

Some of that support came out publicly, as when Defense Secretary Jim Mattis and the chairman of the Joint Chiefs of Staff, Joseph Dunford, told Congress that staying in the deal was in the national interest.

Such cues from advisers can matter politically, because they can affect both Congress and the public — in this case, reinforcing the challenge from within Trump’s own party.

3. Fracturing elite cues make it harder for the administration to send coherent signals abroad.

The Corker comments, the GOP hesitation on the Iran deal and the public airing of internal administration debate continue a theme: The Trump administration finds it difficult to send coherent signals domestically and internationally about its policies.

Theories of domestic support for government policy usually start from the premise that the government has a clear policy for which it wants to build support. But for the Trump administration, it is difficult to know on any given day what official policy is and who supports or speaks for it. And that’s before we ask whether the president’s party in Congress will support him.

What does this mean for signaling U.S. policy internationally? On the one hand, it is harder for Trump to display domestic consensus for his preferred policy, which in this case, seems to be scrapping the Iran deal. Both his party in Congress and other governments don’t know what may happen next or who exactly supports which options. That makes it hard to send a credible message internationally, as Roseanne McManus has noted here at The Monkey Cage.

On the other hand, Trump’s apparent desire to rip up the Iran deal seems to have pushed Congress — which has divided views on the deal itself — to agree the deal was important to preserve.

Why? One reason may be concern for the credibility of U.S. commitments. As Sarah Kreps has shown, elites in democracies often balance domestic disdain for international commitments with the costs of reneging on agreements. States that break their word risk being labeled as unreliable and may lose out on future cooperation with allies. (And in this case, U.S. allies are standing by the deal.)

This might, in turn, signal that Congress is reclaiming some importance on foreign policy — and that the world doesn’t have to view Trump’s moves as a broader signal of American unreliability. Scholars have long debated whether it’s the reputation of a country or its leader that matters — an important question not only for the duration of the Trump administration, but also for how states view potential cooperation with the next president.

4. Elites are holding one another accountable — but don’t expect quick or dramatic results.

On the morning after the election, I wrote that despite partisan polarization:

… most foreign policy elites, in both parties, are internationalist, favor maintaining U.S. alliances and oppose authoritarianism. They will the ones to pay attention to the details of Trump’s foreign policy and sound the alarm if it trends in dangerous directions. Even with Republican control of Congress, these voices may be heard, especially if the divide between Trump and Republican foreign policy elites persists.

Last week, concerns about Trump burst into the open right before an important foreign policy debate. That showed that Trump can’t just get everything he wants on foreign policy. But having elites hold a president accountable can be slow and halting.

For example, some observers called for Corker to hold hearings akin to those that Senate Foreign Relations Committee Chairman J. William Fulbright held on Vietnam in 1966. The Fulbright hearings were an important signal that Lyndon Johnson faced resistance from his own party; it was the beginning of fracturing the elite consensus on Vietnam.

But it was two more years until Johnson decided not to run for reelection, and the war dragged on even under his successor. Presidents can do a lot unilaterally on foreign policy, and Trump may try to work around Congress.

Yet Corker’s comments — like Fulbright’s hearings — will have consequences, even if we don’t immediately see dramatic change.