The proposal would have ensured what's called "reciprocity," in essence requiring states to recognize legally distributed concealed weapons permits regardless of where it was issued.

Currently, there are 23 states that issue concealed weapons permits that Colorado does not recognize. Denver Mayor John Hickenlooper had signed a national ad urging the amendment's failure and had lobbied Senators Michael Bennet (D-Colorado) and Mark Udall (D-Colorado) against the plan.

On Wednesday, Tom Mauser, whose son Daniel was killed in the Columbine shootings, was featured in a full-page ad in The Denver Post, urging Udall and Bennet to reject the amendment as well.

Following the vote, Sen. Bennet issued the following statement:

"In Colorado, law-abiding gun owners have the right to apply for and receive a concealed carry permit. Colorado already recognizes the concealed carry permits from a majority of states, and generally grants reciprocity to states that recognize the permits of Colorado gun owners. Any concealed carry permit holder from another state must follow our criminal statutes, and that would have remained the law if the Thune amendment had passed."

Sen. Udall issued the following statement:

"Since 2003, Colorado has had a relatively relaxed reciprocity statute recognizing the conceal-carry permits of 27 other states. Our experience over the last six years does not lead me to conclude that passage of this amendment would raise the risk of unlawful gun smuggling or other criminal acts. It allows Coloradans to travel elsewhere once they have obtained a concealed permit in our state. It does not encourage irresponsible behavior or absolve anyone from criminal prosecution in Colorado if they use a gun in the commission of a crime."

Mauser, who disagreed with Udall and Bennet's votes, issued the following statement after the amendment was rejected:

"The defeat of the Thune Concealed Carry Amendment is a setback for those who want to overturn common sense gun laws aimed at stopping gun carrying by alcoholics, criminal and other dangerous persons. It is disappointing that Senators Bennet and Udall did not vote the right way today but I look forward to working with them on future initiatives that will protect innocent Coloradans, like closing the gun show loophole nationally which 70 percent of Coloradans supported."

Both of Colorado's senators earlier voted to loosen concealed weapons restrictions in national parks, allowing those with permits to carry their weapons into those areas.

Supporters had argued the measure would have cut down on crime as criminals would be less likely to target victims if they knew they might be carrying concealed weapons. Opponents worried that the amendment would subvert local control and require states and cities with strict gun laws to accept visitors from states and cities with weaker laws.

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