He will now appear before Congress on July 24 instead of July 17.
It is currently unclear why the testimony is postponed.
**Update: Fox News is reporting that there was a “breakdown in negotiations:”
Mueller was slated to testify in public before the Judiciary Committee for two hours or more, followed by another two hours-plus of testimony before the House Intelligence Committee in an open setting.
But there were conflicting details over plans for a subsequent private session. One source told Fox News this week that the Democrats plan to have Mueller testify behind closed doors–yet it remained unclear whether Mueller himself would participate in that setting, or if his deputies would answer questions instead.
**NOTE: This is a breaking report. Please check back for updates.