A relentless global bond rally has Treasury investors pondering what it will take to send benchmark 10-year yields below 2% for the first time since 2016. Rates on 10-year Treasuries dipped lower again on Thursday, after touching about 2.21% the day before -- almost 50 basis points below where they started the year -- amid U.S.-China trade tension and concern over the outlook for the world economy. The flight to safety saw the spread between 3-month and 10-year yields dive to its most inverted level since 2007, as the bond market’s recession signal intensified.