Last year, as it became clear that President Trump was determined to roll back much of what Barack Obama had done as president, we came up with a list of Obama’s 10 biggest accomplishments. It’s not a definitive list, but we consulted scholars, journalists, some of Obama’s own aides and other lists of major legislation and executive actions during Obama’s tenure. We wanted to have some way to distinguish major policy change from more cosmetic or minor moves — getting rid of, say, a regulation Obama had proposed in late 2016 that had not even gone into effect before he left office, for example.

Trump has chipped away at many of Obama’s signature initiatives, such as the tax law the president signed in December that got rid of the requirement in Obamacare that Americans enroll in health insurance or pay a fine. But Trump’s decision, announced on Tuesday, to withdraw the United States from an agreement designed to reduce Iran’s nuclear capabilities could be the first full reversal of one of Obama’s key policy initiatives.

1. The 2009 economic stimulus and the drop in the unemployment rate that followed it.

2. The bailout of the auto companies.

3. The Affordable Care Act (Obamacare).

4. The Dodd-Frank bill that increased regulation of big banks and created the Consumer Financial Protection Bureau.

5. The repeal of “don’t ask, don’t tell” that allowed openly gay and lesbian Americans to serve in the U.S. military.

6. The killing of Osama bin Laden.

7. The drawdown of U.S. troops from Afghanistan and Iraq.

8. The agreement reached between Iran, the U.S. and five other nations to attempt to curb Tehran’s nuclear program.

9. The normalization of U.S. relations with Cuba.

10. The 200-nation Paris climate change agreement that Obama helped negotiate and the slew of additional environmental initiatives that were promulgated through new rules and provisions in the stimulus.

Trump has decided to reimpose U.S. sanctions against Iran that Obama suspended as part of the agreement in exchange for a slew of new restrictions on Iran’s nuclear program. (There is still some question about exactly when the sanctions will go back into place and if new ones will be imposed.)

I used the word could above only because Trump’s actions don’t necessarily end the agreement, which was a deal between Iran, the U.S., Britain, China, France, Germany and Russia. Those five nations have remained supportive of the nuclear agreement, although their calculuses could change with the U.S. now out of it. They are not expected to reimpose sanctions against Iran. So in theory, this agreement could continue in some form, just without the participation of the U.S.

Obviously, the most important question regarding this agreement is Iran’s actual capacity to develop and use nuclear weapons. We don’t know if Trump’s approach will be more or less effective than Obama’s in limiting that capacity. And we don’t yet know how Iran or the other five countries that participated in this agreement will react.

But I think there are four important lessons from Trump’s move on Iran:

1. Trump didn’t get rid of many of Obama’s major policies in his first year, but that doesn’t mean he won’t over time

Just because something didn’t happen right away doesn’t mean it won’t happen. The Iran deal is only the latest example. The Trump administration failed to repeal the Affordable Care Act legislatively, but it has reshaped Obamacare’s insurance marketplaces. The administration is now seeking to change the law’s Medicaid program by getting states to require people enrolled in Medicaid to either have jobs or be in college or a job-training program. Obamacare could be a much different program by 2020, even if it remains the law of the land. Trump is also getting rid of many Obama-era environmental policies, another signature initiative of the last administration.

2. Trump is reversing Obama’s broader vision of foreign policy

Trump’s decision to exit the Iran deal is a big deal in and of itself, but it’s also a good stand-in for a broader doctrinal difference between Obama and Trump: unilateralism vs. multilateralism.

We didn’t list the Paris climate change agreement by itself or the Trans-Pacific Partnership as signature Obama achievements, but the former president was very interested in forming broad, multi-country agreements. I don’t want to downplay Trump’s attempts at diplomacy in North Korea. But Trump’s outreach to Kim Jong Un stands out in part because Trump has otherwise seemed intent on downplaying alliances (ending U.S. participation in the Paris and Iran deals and the TPP, downplaying the importance of NATO, etc.) and having the U.S. make decisions that the international community does not embrace (moving the U.S. embassy in Israel to Jerusalem).

3. The Trump staff shake-up in February and March seemed erratic but made sense in a lot of ways

Trump replaced a national security adviser (H.R. McMaster) and a secretary of state (Rex Tillerson) who viewed this Iran agreement more favorably with new advisers (John Bolton and Mike Pompeo, respectively) who shared the president’s strong skepticism of this Iran agreement. It’s not that McMaster or Tillerson, if they had remained in place, necessarily would have stopped Trump from reimposing the sanctions on Iran. But I assume it’s easier for the president to implement his decisions with staff who are not wary of them and pushing back in private.

4. Trump governs like a Republican, Example No. 6,214

Trump’s decision is big news. And the way he has hinted about this move for more than a year without actually making it is another example of his unorthodox governing style. But remember: Senior Republicans on Capitol Hill strongly opposed the Iran agreement when Obama made it in 2015. The other Republicans who ran for president in 2016 also opposed this agreement and suggested they would get rid of it too. Would, say, Jeb Bush — a more centrist and establishment Republican — have been more likely than Trump to reverse his campaign trail pledge on this issue and try to keep the U.S. in this deal? I think so. But on Iran policy, it’s important to emphasize that Trump’s move was not a particularly Trumpy decision; it was a Republican one.