Illinois was last week poised to become the fifth state to pass an automatic voter registration law.

Despite bipartisan support, however, Governor Bruce Rauner vetoed the measure on the last possible day, Friday.

"I strongly support efforts to encourage greater voter participation in our democracy and share the goals of this legislation," Rauner said in a statement. "Unfortunately, as currently drafted, the bill would inadvertently open the door to voter fraud and run afoul of federal election law.”

But supporters of the law said Rauner's reasons for vetoing were strictly political and dismissed his claims of voter fraud.

“No offense to the governor, but I don’t buy it,” Cook County Clerk David Orr said at a press conference Monday. “We do not have a problem with noncitizens trying to cheat and vote in Illinois. These people do not want to be deported for accidentally registering to vote.”

Illinois's automatic voter registration bill is the latest in an effort to "modernize" and "streamline" the voting system, according to supporters. The basic gist: If a citizen goes to the DMV or any of four other state agencies, the information shared there would be used for voter registration, unless that citizen chose to opt out.

The law—Senate Bill 250—passed the lllinois House by a vote of 86-30 (with 27 Republicans in favor) and the Senate by a 50-7 vote (13 Republicans in favor), giving the state legislature enough support to override a veto, should legislators stick with their initial vote. Rauner also indicated in his statement that he'd be open to a revised version of the law that "protects the integrity of our election system."

Voter registration and voter fraud have been heated topics this election year, including voter ID laws in North Carolina and Wisconsin ping-ponging through courts following claims that they disproportionately affect minority communities. Republican arguments in favor of voting restrictions, like Rauner's opposition to automatic voter registration, generally focus on voter fraud, although many studies have shown that voter fraud is incredibly uncommon in America.

Democrats, on the other hand, accuse Republicans of trying to suppress voting for political reasons. (Many unregistered voters are poor, minorities, and left-leaning.) 

Politics aside, it's informative to look at the actual effects of automatic voter registration. Four states have passed legislation similar to SB250 (Oregon, California, West Virginia and Vermont), though only Oregon has enacted the law thus far. Oregon residents who submitted information to a state agency after Jan. 1 were automatically registered to vote this year, unless they chose to opt out of the process. Oregonians who filled out ID forms at state agencies in 2014 and 2015 were registered in June.

The increase in registration has already been significant. According to PBS, Oregon has registered approximately 51,000 new voters through the DMV alone—nearly half of the state’s total of 115,000 new registered voters so far this year. The state expects to register 200,000 total new voters by November.

The AP reports that Illinois's vetoed bill could have added nearly 2 million voters to the state's voting rolls. (According to the Tribune, 42 percent of voting-eligible African Americans and 33 percent of voting-eligible women in the state are not registered.)

But does increased voter registration and turnout actually affect elections? Researchers Jack Citrin, Eric Schickler, and John Sides wrote in 2008 that contrary to popular belief, neither party would necessarily benefit, even if every single eligible voter in the country voted.

As Sides writes in a 2015 Washington Post column:

[Studying] 246 Senate elections from 1990-2006, only eight outcomes changed when we simulated the impact of universal turnout. In a very close presidential election, as in 2000, universal turnout could have made a difference. But such elections aren’t common.


[We] found that in some states in some election years, non-voters were actually a bit more Republican … That wasn’t the norm, but we should not assume that higher turnout or compulsory voting would always and everywhere benefit Democrats.

Their research lends credence to a hypothesis posed by political scientists for decades, that since the political beliefs of nonvoters do not significantly differ from those of voters, and since most elections are not close, election results would not change whether the turnout is 50 percent or a full 100 percent.

But that's not to say that universal voter turnout has no effect on the political discourse, according to Daniel P. Tokaji, a law professor specializing in elections and democracy. He argues that though turnout may not result in a different election winner, it would likely force elected representatives to recognize the policy wishes of new voters:

A growing body of political science evidence supports this common sense conclusion: that policy makers cater more to the wishes of voters than nonvoters. If we accept that elected officials pay attention to what voters want, then comparing the preferences of voters and nonvoters over issues, not just candidates or parties, matters.