President Obama reportedly is using a unique form of executive action known as the “presidential memorandum” at a historic pace – a tactic that allows him to, technically, claim he’s not over-using executive orders while still pursuing high-level policy changes without involvement from Congress.

A review by USA Today, published Wednesday, shows that, in fact, Obama has issued more memoranda than any U.S. president in history. He’s issued 198 – more than the 195 executive orders from his White House.

The executive action is strikingly similar to an executive order, with only slight differences. But by using the memos, this is how Obama and his advisers have claimed the president is not over-using executive orders.

According to USA Today, when the memos and executive orders are combined, Obama is on pace to issue more “high-level executive actions” than any president since Harry Truman.

As noted in the review, Obama’s most controversial executive action of late – an overhaul of the U.S. immigration system including de facto legal status for up to 5 million illegal immigrants – was done through memoranda.

Those actions already have led to legal challenges – and one judicial rebuke. On Tuesday, U.S. District Court Judge Arthur Schwab, in Pennsylvania, issued an opinion claiming some of Obama’s actions were unconstitutional.

The opinion, though, was delivered in a case not directly related to those actions, and the Justice Department downplayed Schwab’s opinion as “unfounded” and “flatly wrong.”

According to the USA Today review, Obama has used memoranda to take a number of other actions, including directing the Labor Department to collect salary data from federal contractors to see what they’re paying women and minorities, and directing federal law enforcement agencies to trace firearms that are part of federal probes.

The differences between an order and a memorandum are slight. According to the USA Today review, executive orders are numbered and memoranda are not. Executive orders have to cite the law they’re based on, and memoranda do not. Both actions can be used for similar purposes, though.