Mark Kelly and his wife, former Arizona congresswoman Gabby Giffords. (Getty Images)

Mark Kelly, the astronaut husband of former congresswoman Gabrielle Giffords, on Thursday upbraided senators who voted against gun legislation by saying they voted “out of fear.”

 "If that vote had been a secret ballot, I bet you it would have passed with 80 votes,” Kelly told reporters. He was referencing the compromise authored by Sens. Joe Manchin (D-W.Va.) and Pat Toomey (R-Pa.) to expand background checks for gun buyers. It failed to advance in the Senate, with a vote Wednesday afternoon of 54 to 46.

Kelly and Giffords, an Arizona Democrat who was seriously wounded in a mass shooting in Tucson in January 2011, have spent the past few months lobbying lawmakers to support expanding background checks. At a Thursday morning press conference, Kelly recounted their private meetings in recent days with senators.

 “We discussed this legislation with them, we talked with them about how it would work, what it would do, and most of them – actually, almost all of them – said they were in favor of the policy on the merits,” Kelly said. “But many of them were looking to get to a no and it was out of one thing, it was out of fear.”

 When a reporter asked specifically about Sen. Jeff Flake (R-Ariz.), a friend of the couple who voted against the background checks bill, Kelly said he went over the Manchin-Toomey measure line-by-line with Flake. But Kelly said he concluded that Flake was unable or unwilling to understand the legislation.

 “We went over with a piece of legislation in my hand, marked up by me, and I can explain what some of these words mean and I can explain what the bill does, but at some point you cannot help somebody understand it,” Kelly said. “I don’t think he did.”

 Giffords and Kelly have raised millions of dollars for their new political action committee, Americans for Responsible Solutions. Kelly predicted they would have more than one million members before long and said the group would begin airing television advertisements thanking four senators – Susan Collins (R-Me.), Mary Landrieu (D-La.), Kay Hagan (D-N.C.) and John McCain (R-Ariz.) who took political risks to vote for the background checks legislation.

Kelly also said the group would go after senators who voted no, in advertisements and in grassroots activities. He said they were still assessing which senators to focus on, but said, “It’s a target-rich environment.”

"We are not deterred by the actions of a small group of senators who I really feel that history will judge as fearful obstructionists,” Kelly said. “We’re going to take the long view of this fight. We are in this for what Gabby has said is the long, hard haul.”