 It's part of a much larger trend, shifting power from Congress to the executive branch. This is happening along every dimension, and there are too many reasons to talk about Congress being obsessed with reelection, Congress delegating massive authority to the executive because it doesn't want responsibility for the hard decisions, so it can instead focus on reelection and also sit back, see how the president does, and then either take credit or criticize, depending on how things turn out.