Sixteen Democrats pledged Monday to oppose Nancy Pelosi as the next House speaker, escalating the stakes in the longtime Democratic leader’s push to head her party during its first majority in eight years. In a letter to fellow Democrats, 16 current, future or potential House members called to replace Pelosi when the party takes control of the chamber in January. They commended Pelosi as a “historic figure” who led Democrats to some of their most important achievements, but argued that their majority “came on the backs of candidates who said they would support new leadership.” “Therefore, we are committed to voting for new leadership in both our Caucus meeting [on Nov. 28] and on the House Floor [on Jan. 3],” the 16 Democrats wrote. If Democrats end up with 233 House seats, as expected, Pelosi can only afford to lose 15 votes from the caucus and become speaker.