The 14th is a reconstruction amendment btw, it wasn’t drafted or ratified by the founders.

The actual article is in The Hill

The president can’t just appoint whoever they want. Officer commissions have more oversight than say judicial appointments. They have to be approved by the Senate (eg this situation) and also have to meet requirements for the position/rank set out in regulation by congress. So a president could theoretically only promote the most conservative officers in the pool, but it’s already a small pool.

Even so, as we see here, it only takes one senator to block promotions. This isn’t even a fillibuster, the Senate passes this routine stuff through bulk unanimous consent.

The podcast Ultra by Rachel Maddow goes into the history of this period and is really good