Why did Republicans vote against keeping guns from people on the terrorist watch list?

They didn't. They voted against a motion to waive all budgetary discipline from the amendment that does this. The amendment was an change to the bill that cripples Obamacare and defunds Planned Parenthood. A bill that Obama has already threatened to veto, and gun control has nothing to do with the rest of the legislation.

Thank you for selecting this as best answer, because it is 100% accurate.

Because there is no adjudication of the No Fly List. Republicans don't believe the government should be able to negate a citizen's 2nd Amendment rights by having a bureaucrat writing the citizens name on a list.

Because it is unconstitutional. Lets say someone's identity was stolen and ended up on the list by mistake. Does that give the government the right to deny them a firearm? What if you ended up on the list? Would you be good with not being armed in a sick world like this? Convicted felons have restrictions. Suspects have rights. Learn the difference.

Probably because there are high profile cases of people being put on the list without either cause nor due process. We've put infants on the list for having similar names to known terrorists, for example.

Since Obama is still president, the Republicans are voting against every bill he is trying to pass. They just slam the brakes and make sure nothing gets passed in congress

When you buy a gun there is an FBI background check. I would hope the FBI would reject sales to known or suspected terrorists.

You don't need to pass any new law.

Because they're idiots just like the rest of the two party cult system.

Free enterprise

That's what I'd like to know! I guess the NRA told them to.

When guns are outlawed only outlaws will have guns.