“But that,” he said, “doesn’t mean it isn’t happening.”

Republicans have typically countered such accusations with one of their own: That Democrats are overhyping the possible impact on voters.

A recent report by Reuters seems to buttress the Republican argument, finding that in states that have had similar laws on the books for a few years — Indiana and Georgia — turnout and registration actually increased after the laws took effect.

That report, however, does not take into account certain variables. For instance, 2008 was historic, a presidential election that drove up voter turnout around the country.

“We don’t know any more than we did before,” Charles Stewart III, a political science professor at the Massachusetts Institute of Technology who specializes in elections, recently told the news site ProPublica. “Any change in requirements relating to voter registration and access typically has a change by one or two percentage points. When you’re talking about that size, it’s very hard to tease out the data.”

Missouri Republicans pushed through a photo ID bill in 2006 that was later struck down by the state Supreme Court. It ruled that the law amounted to a “heavy and substantial burden on Missourians’ free exercise of the right of suffrage.”

To move forward, Republicans have to put a change to the state’s constitution on the ballot. If passed by the legislature, the measure would appear on statewide ballots in 2014. An implementation bill, laying out what type of ID could be used to cast a ballot, would have to pass separately and go to the governor.

Both cleared a House committee Tuesday on a party-line vote.

The state would cover the cost of obtaining a photo ID for those who are unable to do so. But the state would not pay the cost of gathering underlying documents, such as a birth certificate, needed to get an ID.

And while it would allow those unable or unwilling to get a government-issued photo ID to vote, they would have to cast a provisional ballot. According to the secretary of state’s office, only 25 percent of provisional ballots cast in 2012 were ever counted, since they can be disqualified for a number of reasons ranging from a signature not matching one on file or a mistake in how the provisional ballot’s affidavit was filled out.

Driver’s licenses, state-issued non-driver’s licenses and military IDs would qualify under the proposed legislation. Some other forms — such as a university ID — would not.