Emanations and penumbras is exactly how Levin is trying to change be the plain language of the Constitution, except the emanations and penumbra's don't come from the Constitution itself, but rather from a DOJ policy.
First, he says:
The DOJ has taken the position under both parties that you cannot indict a sitting president because it would cripple the executive branch and make his ability to defend himself effectively impossible.
That's the emanation, and...
3. Given the DOJ's position, and the Supremacy Clause in the Constitution, I would argue strongly that the idea that a president cannot be indicted at the federal level because it would cripple the executive branch, but can be indicted by local DAs, would have exactly the same effect as a federal indictment, except there are thousands of local and state prosecutors making the crippling of a president even more likely.
...There's the penumbra. I'd point out that even if Levine's argument is correct, it certainly would not require the president to have the unilateral decision to prevent his own indictment. Rather, the courts could adjudicate that limited issue of presidential immunity while in office.
His reasoning then gets even worse:
4. FURTHERMORE, if indicted and even convicted, the idea that a president cannot pardon himself from state charges is absurd, again, not only because of the Supremacy Clause, but the same considerations that apply to a federal conviction would obviously apply to a state conviction.
What Levine is missing is that the problem he identifies - the President being unable to perform his duties if convicted - can be solved by simply having the courts stay the prosecution until he is out of office. That's almost certainly the route they would take, and makes far more a sense than the lunacy of the president having unfettered power under the Constitution to pardon himself for any crimes he might commit in office.
If you take Levine's argument at face value, the president could rape and murder women with impunity because he could immediately pardon himself.