Candidates have to be confirmed/approved by the Senate. But Trump wants to bypass this stage.
Hegseth:
The Princeton- and Harvard-educated Hegseth, who served as an Army infantryman in Iraq and Afghanistan as a member of the Minnesota National Guard, also played a role in episodes that roiled the Pentagon and involved Trump’s defiance of military norms during his first term in office.
From WaPo:
...But that’s the test: Do Republican senators, tasked with balancing out the power of the executive branch, dare contest Trump’s nominee?
Trump has already introduced a test for his party’s Senate caucus, demanding that they allow him to make appointments to his administration and the courts while the chamber is recessed, bypassing the requirement of Senate approval. Some Republican leaders quickly agreed. They, like many in their party, appear to think that protecting their individual power as senators is preferable (or at least easier) than protecting their institutional power.
That this issue emerges again around the Department of Defense is striking, particularly given other indications that Trump plans on upending the department. The Wall Street Journal reported Tuesday that Trump was considering the formation of a board that would evaluate leadership within the military, likely to lead to a purge of those seen as failing to meet standards set by the administration. Loyalty to Trump and his politics would almost certainly be an implicit standard, if not an explicit one.
As commander in chief, he has the power to fire military leaders. What’s proposed here is different, though. It’s a remaking of the institution, a jettisoning of the slow accretion of authority within the armed forces — with a Fox News host nodding along from his desk at the Pentagon.
Hegseth’s nomination will probably not be as easy as Ingraham and Chaffetz hinted that it should be. Even if it isn’t, Trump is signaling what he wants: a legislative branch that won’t counteract his demands, however dubious, and a military that will operate strictly within the boundaries that he sets, from the top down.
This is, to put it mildly, a deviation from how past presidents have wielded power.