(Fox News) Sens. Marco Rubio, R-Fla., and James Inhofe, R-Okla., joined three other Republican senators threatening to filibuster any new restrictions on guns Thursday.

The two senators added their signatures to a letter previously signed by Sens. Rand Paul, R-Ky., Mike Lee, R-Utah, and Ted Cruz, R-Texas, vowing to protect the Second Amendment.

The letter, which was originally sent to Senate Majority Leader Harry Reid on March 22, outlines the senators’ intent to “oppose any legislation that infringe on the American people’s constitutional right to bear arms.”

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