There's been a continued series of hawkish comments from the Fed, and there's supply pressure with today's five-year auction. All of this is going to put downward pressure on Treasury prices.
The spread supply had been a factor weighing on the Treasury market and when the 10-year TIPS auction didn't go terribly well, that compounded the issue.
You have seen a pretty significant rise in open interest in the Treasury futures market since the middle of last month as prices have declined, suggesting a pretty substantial short base out there, so we've held our footing so far this week.