American presidents are fairly weak as these things go. Really, he can do three things without Congress. First, use the military outside the United States. Second, issue executive orders ... as long as said orders do not include unilaterally sequestering funds or overturning existing regulations. (The Administrative Procedure Act of 1946 greatly limited presidential power in this regard.) Third, administer the executive branch.
And in this respect, the Obama administration has fallen down on the job. The damn website is an own-goal. More so since Obamacare is working fine in states that did the job themselves.
The wrong lesson to take away from this is that state governments do things better than the feds. There is no evidence for that, beyond vague small-is-beautiful prejudices.
The right lesson is that President Obama right messed this up for no particularly good reason.
Sadly, however, it is not true that presidents with administrative experience turn out to be good managers (viz James Earl Carter) or that ones without it turn out to be bad ones (hey hey LBJ). So there seems to not be an easy metric to judge how well somebody will do as an administrator before they actually need to administrate. Worse yet, overseeing the creation new stuff is a very different thing from managing an existing operation.
But ex post, even though Obamacare going to work out in the medium run (my apologies, Republicans, but liberalism is not over and a defective website gets nobody killed) the unnecessary mess seems to me to have shown the President to be deficient in one key skill for an executive: project management. The historical record should reflect that.
Am I being too harsh?