Americans for a Strong Defense, one of the outside groups, continues to focus its campaign on states with undecided senators, such as Alaska, Louisiana and Arkansas.
"We found that our grassroots efforts have intensified since Chuck Hagel's disastrous confirmation hearing," said spokesman Ryan Williams. "People are more concerned now about his nomination given the lackluster performance he delivered in front of the Senate Armed Services Committee last week."
Williams, who recently worked for Republican presidential nominee Mitt Romney, said the group has reached out to local leaders to pressure senators while the organization churns out a steady stream of news releases critical of the nominee.
Danny Gonzalez of the group Move America Forward, a pro-military organization, said his group's approach is to "fire up the grassroots and get those people motivated. We're definitely going to notify our list about which senators have publicly stated they are thinking about supporting him, calling their offices, faxes, email."
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.