Direct Tax not Cap-n-Trade of GHG in US ?

Is there a possible movement for a direct tax of GHG emissions at Federal level in the US instead of a cap-n-trade system similar to RGGI and EU ETS?

When I was in CA last fall, government officials were undecided whether ARB-32, a CA state-wide GHG regulation, would use a direct tax or cap-n-trade regulatory mechanism. At the time, I was surprised given all the general talk about the merits of cap-n-trade.

The Chairman of Exxon recently reversed Exxon's official position from cap-n-trade to direct regulation.

A regulation lawyer told me this was a move by big oil to box in the coal companies. The politicking has begun in earnest.