In October 2014, Senator Kay Hagan missed a Senate Armed Services Committee meeting to attend a fundraiser. There is still no credible explanation from her office as to why she did this:
http://www.cnn.com/2014/10/10/politics/kay-hagan-armed-services-wrap/
The meeting was a classified briefing on ISIS and other national security threats with the Director of National Intelligence and other senior officials. Apparently for Senator Hagan, talking with donors was more important than hearing what these officials had to say about an organization that has terrorized Syria and Iraq, ruthlessly beheaded American and British hostages, and dragged the United States once more into engagement in Iraq.
We can blame this on Senator Hagan (her adversaries certainly will) or we can blame it on a campaign finance system that makes this kind of thing happen.
None of us can rightly criticize any incumbent for this conflict of commitment without also criticizing them for refusing to enact meaningful campaign finance reform. And that most of them are unwilling to do.