Reduced to the most simplistic of considerations, bond market price movement is all about supply and demand. The same is true of just about anything with a price, but things can get weird when it comes to Treasuries/MBS. For instance, one might not necessarily think much of the corporate bond market as having a direct impact on Treasuries, but it's actually one of the most common behind-the-scenes considerations (we have a primer that explains why). On weeks where corporate bond issuance coincides with Treasury issuance, default selling pressure is easy to reconcile. That's the case so far this morning with multiple corporate deals announced and Treasury issuance looming.
In term of trends and the bigger picture, bonds have quickly reconsidered what looked to be a range breakout last Wednesday. Yields briefly dipped below 3.42%, but are now back well within the 3.42-3.62 range that defined the first half of December and most of January.
With the Fed in its blackout period (no speeches in the 12 days leading up to a Fed announcement, in this case, on Feb 1) and a relatively lighter econ calendar this week, it remains to be seen if markets will have enough inspiration to challenge the range before Fed day.