Senators Express Regret Over Opposing Gun Reform After Sandy Hook
• Four current senators and three former senators regret opposing gun reform after Sandy Hook shooting
• They felt pressured by NRA supporters and the NRA itself at the time
• Sen. Heidi Heitkamp was described as "defensive, unkind" in meeting with victim's mother
• Sen. Martin Heinrich said he now sees gun violence as "everyone's issue"
• Heitkamp said she was "extraordinarily sorry" for leaving impression she didn't care about victims