There is perhaps no other politician on the national scene right now who has a clearer identity than Sen. Elizabeth Warren (D-Mass). She is the unvarnished id of her party, providing that gut check, that heart part of every issue that others can't seem to muster. And she does it in what appears to be carefully planned exchanges and performances.  (Perhaps only Chris Christie rivals her YouTube greatest hits collection).

This week provided yet another example.

In one corner was Sen. Rand Paul (R-Ky.) -- not present, but there in spirit -- and in the other, Warren, as she questioned Anne Schuchat, the director of the CDC’s National Center for Immunization and Respiratory Diseases about the safety of vaccines at a Senate hearing, a forum she has quickly mastered.

Here's the simple question and answer:

“Is there any scientific evidence that vaccines cause autism?” Warren asked.
“No,” said Schuchat.
“Is there any scientific evidence that vaccines cause ‘profound mental disorders’?” she asked, quoting her colleague from Kentucky directly.
“No,” responded Schuchat, “but some of the diseases we vaccinate against can.”

Liberals swoon at these types of exchanges, which Warren serves up often. Blogs reported that Warren had publicly shamed Paul, who caused a stir with his Michele Bachmann-esque quotes on vaccines and has since proclaimed that he doesn't understand what the big deal was when he offered that he had heard of "many tragic cases of walking, talking, normal children who wound up with profound mental disorders after vaccines." Warren's strategic skirmishes highlight why some liberals so desperately want her to run -- a move she is highly unlikely to make.

But her speeches and prosecutorial approach to hearings also highlight why she wouldn't want to run for president. White House bids can be soul-sapping, years-long exercises in airbrushing and sanding off the rough edges. Even bits of biography are poll-tested. It's a grind with no guarantees except constant message massaging and crises.

We've called Warren a much, much better version of John Edwards. Another, more apt example -- given that it appears that she will make her career in the Senate -- is the man who once held her seat, Ted Kennedy. Kennedy was the last liberal lion with a national footprint. Similarly, as a senator Warren will be a player in 2016 and beyond, forcing others to "go there" on her issues as the highlight reel grows.

This is not to suggest Warren has attained the longtime senator's level of respect or that she has done in two years what he did in 47 -- just that they are cut from the same cloth and serve similar roles in today's Senate. It's no coincidence they both come from perhaps the bluest state in the country.

While everyone wants to know who is running for president in 2016, Warren knows her influence in the Senate can be quite powerful, and that goes double if she doesn't run.

Video of exchange below: