WASHINGTON On March 21, Nevada Gov. Brian Sandoval (R) vetoed legislation that would have automatically registered eligible voters when they sought services from the Department of Motor Vehicles. The veto made Sandoval the third Republican governor to sink automatic voter registration legislation and all three of them have seats that will be up for grabs in the next two years.

New Jersey Gov. Chris Christie (R) vetoed similar legislation twice once in 2015 and again in 2016. Illinois Gov. Bruce Rauner (R) also vetoed legislation in 2016. Christie, the most unpopular governor in the country , is term-limited and will not be on the ballot again this year. Sandoval will be term-limited out of office in 2018, while Rauner is up for re-election next year.

Its not surprising that Republican governors in those states lack enthusiasm for automatic voter registration, which tends to benefit Democratic candidates. Hillary Clinton won all three of those states in the 2016 election , and Democrats see them as top targets for next years midterms. New Jersey will vote for a new governor this November, and Democratic candidate Phil Murphy, a Goldman Sachs banker who has endorsed automatic registration, is currently leading the polls.

The issue is also a priority for Democrats in states where they are looking to consolidate power in 2018. Thirty-eight Republican governorships are up for election next year, including six in states Clinton won last fall. Democrats hope that President Donald Trump s poll numbers will remain low and help drag down the partys candidates. In states like Washington, Democrats just need to win a small number of seats to get full control of the state legislature. While automatic voter registration may not be at the top of voters minds, Democrats will almost surely advance the issue anywhere they claim a governors house and legislature next year.

Of all the possible reforms meant to increase voter registration and participation, few have taken off in the past three years as dramatically as automatic voter registration. Since 2015, six states and the District of Columbia have enacted automatic voter registration. Oregons state legislature approved it first, followed by Californias just seven months later. In 2016, West Virginia, Vermont and Washington, D.C., enacted the reform through legislation as well, while Connecticut Secretary of State Denise Merrill worked out an agreement with the state DMV to begin automatically registering voters. Alaska voters approved a ballot initiative making registration automatic last November.

Bills have been introduced in at least 30 states in the past two years. Sen. Bernie Sanders (I-Vt.) introduced federal legislation in 2015 to mandate automatic registration nationwide, though that never went anywhere. Both Clinton and then-President Barack Obama endorsed the reform in 2016. And progressive policy groups like the State Innovation Exchange and the New York-based nonprofit Brennan Center for Justice are working to advance legislation across the country over the next two years.

Really, in two years time this has gone from nowhere to quite a few states, Jonathan Brater, counsel for the Brennan Centers Democracy Program, told The Huffington Post. And theres even more legislation on the horizon.

Massachusetts, Rhode Island and Illinois, despite Rauners previous veto, top the list of states where legislation could be passed and signed into law. In Nevada, the issue is still alive, as Sandovals veto means the legislation will go directly before state voters on the November 2018 ballot. Colorado, like Connecticut, has already started the administrative process of moving to automatic voter registration.

The rapid rise of automatic registration as a high-profile issue stems from both partisan politics and structural changes that previous voting reforms brought about.

On the partisan side, Democrats feel the need to press reforms to make it easier to vote due to an earlier wave of Republican measures that sought to make it harder to vote, such as voter identification requirements, after the GOP won full control of 21 states in 2010.

If automatic voter registration leads to increased turnout, it would likely be a boon for Democrats in states with large numbers of unregistered eligible voters particularly younger people, Latinos and African-Americans, who tend to lean Democratic.