Esther George, Federal Reserve Bank of Kansas City President, says it's time to get started on scaling back bond buying even though the delta variant poses a risk. Russ Koesterich, BlackRock Global Allocation Fund Portfolio Manager, expects yields back up a bit by year's end. Darrell Cronk, says September is going to be a white-knuckle event. Sam Stovall, CFRA Chief Investment Strategist, says the market is vulnerable to some sort of upset.