McCaskill has been a stalwart for transparency on the committee. Republicans Kelly Ayotte of New Hampshire, John McCain of Arizona and David Vitter of Louisiana have joined the opposition, but all three voted to conduct the markup proceedings behind closed doors in 2013.
The strongest support for transparency from lawmakers came in 2010 and 2011. In each of those years, nine senators voted to keep the doors to the full committee markup open, but they were still a minority.
Levin does not intend to respond to the Standing Committee’s most recent letter, according to spokeswoman Tara Andringa.