Already, many of Trump’s moves, especially on the environment and immigration, have been challenged in court, with mixed results. In the early months of his presidency, the administration often tried to cut corners and was stopped short by judges. Over time, though, the White House has become more careful about following federal rule-making procedures.

But what judges don’t eliminate, a new president might undo. Democratic contenders are promising to reverse many of Trump’s orders in their own first 100 days in office. Nearly every candidate has said that she or he would rejoin the Paris Agreement, for example. But even if Trump were to win reelection and then be replaced by a member of his own party in 2025, it’s easy to imagine a Republican who is less Trumpist in ideology reversing some of Trump’s orders on trade and immigration.

Not every executive action is so fragile. Trump’s withdrawal from the TPP is likely permanent. But it’s easier to tear down with executive orders than to build. The administration negotiated a replacement for NAFTA, inelegantly dubbed the U.S.-Mexico-Canada Agreement, but it still awaits congressional approval, and Democrats in the House are showing no urgency.

Read: The high-water mark of the Trump presidency

These potentially ephemeral achievements, and the rickety legacy they compose, are surprising because Trump began his presidency with two years of control of the House and the Senate. Republicans have since lost the House, though the Senate remains essential to the project of installing conservative judges on the bench. But Trump squandered most of that time. Despite sizable majorities, he did not obtain funding for his border wall, or enact any of the other legislation he promised in his “Contract With the American Voter,” save tax cuts. Only after Democrats won the House did Trump try to force Congress to fund the wall, and he met with predictable failure. Instead, Trump wasted months of his first two years on a series of unsuccessful attempts to repeal and replace the Affordable Care Act.

Here, too, Trump is echoing the mistakes his predecessor made. Obama entered office with Democratic control of the House and the Senate. He quickly passed a large (though arguably not large enough) economic-stimulus package. Then, like Trump, he spent months on a bruising fight on health-care reform. He paid a great price for that: It both helped foment the 2010 midterm Republican rout and also cost the president the chance to focus on other progressive priorities, such as job creation or gun control. Obama, however, managed to pass the ACA, while Trump’s quest to tear it down failed.

Once Republicans took over in 2011, Obama found his hands tied, and he began to rely more and more on his “pen and phone,” as he described executive orders. The result was a series of steps that looked like wins at the time, but that have been easy targets for Trump to reverse. Obama himself understood this, and offered Trump some helpful advice after his 2016 victory. “My suggestion to the president-elect is, you know, going through the legislative process is always better, in part because it’s harder to undo,” he said.