Republican presidential candidate Ted Cruz speaks in New Hampshire. "I will apologize to nobody for using every tool we can to encourage Iowa voters to come out and vote" Cruz told reporters earlier this week. (AP Photo/Elise Amendola)

Voter fraud is, for all intents and purposes, practically nonexistent. The best available research on the topic, by Loyola Law School professor Justin Levitt, found only 31 credible incidents of voter impersonation in an investigation of over 1 billion votes cast.

But that hasn't dampened Republican efforts to pass a spate of strict voter ID laws since 2008. And it hasn't hurt the public's overall enthusiasm for those laws, either.

But the results of a new working paper from political scientists at University of California, San Diego suggest folks may want to consider. The researchers analyzed turnout in recent elections -- between 2008 and 2012 -- in states that did and did not implement the strictest form of voter ID laws. They found that these laws consistently and significantly decreased turnout not just among traditionally Democratic-leaning groups, like blacks and Hispanics, but among Republican voters too.

The findings are notable because they're some of the first using data in elections that took place after some states implemented photo ID requirements to vote. Previous studies on the effects of these laws showed mixed results. A 2014 report by the Government Accountability Office examined 10 of these studies. Five showed no significant effect of voter ID laws on turnout, four found a significant decrease in turnout, and one found, paradoxically, that the laws increased turnout.

But each of these 10 studies was of general elections that took place before 2008. Most of the strictest ID laws were passed after that, so the ability of earlier research to gauge the impact of these laws is extremely limited.

That's what makes the current research so important. The study's authors controlled for a wide variety of factors known to affect voter turnout -- age, education, income, marital status, etc.

They also controlled for other state laws that affect participation, like early voting. And they considered less-tangible aspects that influence turnout, like the competitiveness of races and whether the election was held during a presidential contest year or an off-year.

After controlling for all these factors, they found "substantial drops in turnout for minorities under strict voter ID laws." Their analysis suggests that turnout for Latino voters was suppressed by 10.8 points in states with strict photo ID laws, compared to states without them. For multiracial Americans, the drop was 12.8 points.

The laws also increased the participation gap between whites and non-whites. "For Latinos in the general election, the predicted gap from whites doubled from 5.3 points in states without strict photo ID laws to 11.9 in states with strict photo ID laws," the study found. For black voters in the primaries, the strict photo ID laws caused the gap with white voters to almost double to 8.5 points.

The net effect of all this? "Democratic turnout drops by an estimated 7.7 percentage points in general elections when strict photo identification laws are in place." Democrats weren't the only ones affected, either. The data showed that Republican turnout was depressed by 4.6 percentage points too.

But the laws disproportionately affected Democratic voters. "The turnout advantage of those on the right is three to five times larger in strict photo identification states, all else equal. These results suggest that by instituting strict photo ID laws, states could minimize the influence of voters on the left and could dramatically alter the political leaning of the electorate. "

These are strong claims, and proponents of voter ID are likely to take issue with them. One common argument is that black voters actually turned out at a rate higher than whites in the 2012 election, after several states implemented strict ID laws.

But this doesn't answer the question at all: turnout among black voters may have been even higher had the strict photo ID requirements not been put in place.

Another common argument is that few people actually lack a drivers' license or other type of photo ID that some states requirement. This hinges partially on your definition of "few." Estimates of the percentage of registered voters without valid photo ID range from one to 11 percent. But regardless of your preferred metric, it's unquestionable that we're living in an era of razor-thin electoral margins. A one percentage point difference can be huge when you're talking about an election with a margin of victory of say, 0.3 percentage points.

"Strict photo identification laws have a differentially negative impact on the turnout of Hispanics, Blacks, and mixed-race Americans in primaries and general elections," the UCSD study concludes. "Voter ID laws skew democracy in favor of whites and those on the political right."

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