But what’s most interesting is the way the president is choosing to flex his muscle compared with his predecessors. Past presidents have frequently tested the limits of their powers—and of the Constitution—on national security, war powers, and push-pull interactions with the legislature. But Trump seems to be pushing against the limits of his presidential power almost entirely to protect himself. “He certainly uses presidential power for personal purposes,” says Julian Zelizer, a professor of history at Princeton. “That’s the place he uses it more aggressively—to protect himself, to protect his inner circle. That’s clearly where he’s most assertive.”

By even publicly discussing a self-pardon, Trump is breaking new ground. Richard Nixon apparently considered the idea late in the Watergate scandal, but the Office of Legal Counsel (OLC) concluded he could not do so, and he did not try. Instead, he resigned, and his successor, Gerald Ford, pardoned him. Yet unless and until Trump actually tries to pardon himself, or refuses a subpoena, or shoots a former official and tries to resist arrest, the actual limits of executive power will remain unknown.

“Most recently he’s at least openly talking about things beyond the boundaries of where other presidents were willing to go,” says George Edwards III, a professor of political science and presidential studies at Texas A&M. Other presidents have tried to shield the West Wing from scrutiny, he notes, “but most presidents step way back from that when it comes to something in the realm of criminality, and of course most presidents are not seriously under examination.”

Presidential privileges, once established, tend to persist. Opinions diverge about where to date the beginning of the expansion of the president’s power. Abraham Lincoln claimed vast powers during the Civil War, including allowing detaining prisoners without appearing before a judge. Teddy Roosevelt consolidated federal power. A common conservative argument pins the most dangerous expansion on Franklin Roosevelt’s New Deal, and World War II only expanded the president’s ambit. Several years ago, the historian Robert Dallek suggested that John F. Kennedy had begun a new era. Liberals point to George W. Bush’s vast assertions of power after 9/11; conservatives point to a variety of moves by Barack Obama, often focusing on his own military moves overseas. Libertarians, civil and otherwise, shake their heads in despair and say both groups are right.

It’s worth considering where these expansions took place. Franklin Roosevelt seized new powers over the economy, first to fight the Great Depression, and then for the war effort. This gave the executive branch new sway over regulating business and agriculture, under the cover of interstate commerce. He also infamously tried to pack the Supreme Court in order to bless some of his expansive assertions of power, and while that failed, the justices became more amenable to Roosevelt’s expansions afterward. Some of these powers slowly abated, while others remained. Harry Truman attempted to seize control of the steel industry in 1952. Price controls generally disappeared, though Richard Nixon briefly froze wages and prices to combat inflation.