For all of Sen. Elizabeth Warren's (D-Mass.) popularity among Democrats and all the speculation that she could challenge former State Secretary Hillary Clinton for the 2016 Democratic nomination, there's Salon's Joan Walsh to explain why Warren shouldn't run:

I ... worry that transforming Warren from a freshman senator with an admirable, ambitious and crucial agenda of financial regulation and economic equity into a presidential candidate potentially hurts Warren, as well as her agenda. Working her legislative priorities in the glare of the global presidential media spotlight will at least change, if not thwart, her priorities.

In essence, Walsh is arguing that Warren's "crucial agenda" in the Senate wouldn't hold up under the national spotlight because it may not have national appeal.