Looks like Senator Richard Burr (R) seems to be obstructing the Investigation

"The committee has yet to issue a single subpoena for documents or interview any key witnesses who are central to the probe, the sources said. It also hasn’t requested potentially crucial evidence — such as the emails, memos and phone records of the Trump campaign — in part because the panel’s chairman, Sen. Richard Burr, R-N.C., has so far failed to respond to requests from the panel’s Democrats to sign letters doing so, the sources said."...