Cooper Howard with Charles Schwab says it's notable that markets didn't respond harshly to the Moody's downgrade on the U.S. credit rating. He believes the timing is interesting given Congress's debate on the tax bill. However, Liz Ann Sonders warns downside pressure is very much in play with markets "at the mercy of headlines." That said, Liz Ann believes a risk-on mentality is a bullish push forward.