It's relevant because Reagan renewed the Nixon-era drive towards assertions of executive power to advance national security.
You might even think he did it for good reasons, e.g. because the threat of communism was sufficiently dire that it really did justify a suspension of the usual legal niceties in order to defend the U.S.'s national interests. The point is not "Reagan was wrong", but rather a more descriptive one: Reagan pushed the boundaries of executive power. Maybe that's good, maybe it isn't. But as a descriptive matter, Reagan is an important link in the modern chain of presidents broadening executive power on national-security grounds.
I don't think this is particularly controversial even among conservative historians. The debate is over whether Reagan's general tendency towards a strong-executive, law-and-order-via-military-if-necessary position (shared with folks like Edwin Meese) was justified, not over whether it was the case. Even going back to his pre-presidency days, for example, conservative historians typically argue that Reagan's declaration of martial law in Berkeley in 1969, in which he sent in the national guard to put down a series of protests, was necessary to maintain order and prevent subversive elements from gaining a foothold. Nobody actually argues that he didn't do so, or that it was some kind of situation where he was tricked into it. He was pretty explicitly a national-security hawk in favor of a strong executive.
You might even think he did it for good reasons, e.g. because the threat of communism was sufficiently dire that it really did justify a suspension of the usual legal niceties in order to defend the U.S.'s national interests. The point is not "Reagan was wrong", but rather a more descriptive one: Reagan pushed the boundaries of executive power. Maybe that's good, maybe it isn't. But as a descriptive matter, Reagan is an important link in the modern chain of presidents broadening executive power on national-security grounds.
I don't think this is particularly controversial even among conservative historians. The debate is over whether Reagan's general tendency towards a strong-executive, law-and-order-via-military-if-necessary position (shared with folks like Edwin Meese) was justified, not over whether it was the case. Even going back to his pre-presidency days, for example, conservative historians typically argue that Reagan's declaration of martial law in Berkeley in 1969, in which he sent in the national guard to put down a series of protests, was necessary to maintain order and prevent subversive elements from gaining a foothold. Nobody actually argues that he didn't do so, or that it was some kind of situation where he was tricked into it. He was pretty explicitly a national-security hawk in favor of a strong executive.