A planned Senate Judiciary Committee vote on William P. Barr’s nomination to serve as attorney general has been delayed for a week, as Democrats continue to raise concerns about whether he will allow special counsel Robert S. Mueller III to finish his probe and publicize the results unimpeded. The delay, which is customary for high-profile nominations, is not expected to impede Barr’s eventual chances of being confirmed by the full Senate. But it is the latest reflection of the deep partisan tension surrounding Barr’s nomination, most of which centers on Democrats’ desire to protect Mueller’s probe from being unduly constrained....