The various public clashes between McCain and Cruz have been widely interpreted as a sign of GOP fragmentation between establishment figures and tea partyers who wield disruption in service of conservative principles. McCain famously called Cruz and similar Republicans "wacko birds" before apologizing.
For perspective, this is only one nomination. Defense Secretary Jim Mattis credits McCain with "leading the effort" in Congress to fill vacancies at the DoD and told reporters that McCain is "doing everything he can to fill those numbers."
The White House has been slow to advance its nominees to the Senate for confirmation and — to the GOP's growing anger — Senate Democrats have been using delay tactics to slow confirmation when the names arrive.
Trump first announced his plans to nominate Newman on March 21 and sent his name to the Senate Armed Services Committee on April 28, where there's been no action since.
According to people familiar with the matter, Newman, during an office visit with McCain after his nomination, expressed he was against registering women for the draft. That has fueled the impasse and fueled speculation the White House would withdraw Newman's name.
A White House spokesman declined to comment and Newman did not return calls seeking comment.
Aaron Mehta and Leo Shane III in Washington, D.C. contributed to this report.