Changes to state voting laws -- some geared toward expanding access to the polls, some intended to prevent fraud and thus making it harder to vote -- have been proliferating in recent years. But how much of an impact will they have on the 2016 elections, from the presidential contest on down?

While it's still early, a review of states that have changed their election laws since the last presidential cycle suggests that the impact will be felt widely by voters but won't necessarily affect the outcome of contests in more than a few states.

All told, 17 states -- most of which are solidly conservative -- have tighter voting laws in place this year, according to the Brennan Center for Justice. The new laws range from strict photo ID requirements to early voting cutbacks to registration restrictions. Such laws are often decried by opponents as harmful to minorities and young voters -- groups that are more likely to vote Democratic.

But many of the states that have implemented such measures aren't considered competitive in the presidential election. Nor do many of them have competitive gubernatorial elections this year.

Some states have done the opposite and expanded voter access. Most of these states are solidly Democratic in presidential contests, but a couple (Oklahoma and Utah) are Republican strongholds, and one (Colorado) is a swing state.

It's in the states that have both changed their voting laws and have competitive contests this fall that we'll see the biggest impact on who wins.

One of those states is North Carolina. In 2013, the Republican-dominated legislature passed a far-reaching voting law that, among other things, eliminated same-day voter registration, reduced the period for early voting and instituted voter ID requirements. The controversial law has since been upheld in federal court but that ruling is being appealed.

In the meantime, North Carolina is a presidential battleground state and has an ideologically tinged, competitive gubernatorial election this year. Either of these races, or other statewide contests, could easily be decided by narrow margins, with the new voting laws possibly spelling the difference between victory and defeat.

"They clearly have the potential to suppress turnout among Democratic-oriented segments of voters," said Ferrel Guillory, a longtime observer of state politics at the University of North Carolina. "Will that happen? Perhaps. And perhaps Democratic allies will respond with an extra measure of energy in voter turnout activity. A lot depends on how much the Clinton campaign invests in North Carolina."

Meanwhile, Ohio -- the mother of all electoral battlegrounds, as well as home to a key U.S. Senate contest this year -- has also seen its election laws fluctuate in recent years.

In 2014, the GOP legislature approved several provisions, including cutting six days of early voting -- a move that effectively eliminated the "golden week" in which residents could both register and cast their ballot. But after a legal back-and-forth, a federal judge struck down the law.

If the ruling stands, experts believe that "it will help Democrats, especially at the top of the ticket," said Bill Binning, a former Republican official and an emeritus political scientist at Youngstown State University. However, an appeal could be heard and ruled on before the election, leaving a lot at stake.

Wisconsin is another state where litigation could have an impact on Election Day. The state is always hotly contested in the presidential race, and it should be especially crucial this year as Republican nominee Donald Trump seeks to boost working-class white turnout in the Midwest.

Republican Gov. Scott Walker and the Republican legislature enacted photo ID requirements and a shorter early-voting period. But Democrats are challenging the changes. They argue that under the federal Voting Rights Act, the legal system has to look at all of the election rules in a state, rather than just the specific provision being challenged, when determining whether the law treats all voters fairly.

"In Wisconsin, you have a big voter ID component, but the plaintiffs refer to four or five other rules changes in the state, arguing that these -- plus voter ID -- in their totality lead to a denial of opportunity," said Edward B. Foley, director of the election law program at Ohio State University.

In this and similar cases, "you're starting to get lower-court rulings, but ultimately, the Supreme Court will have to weigh in," said Foley.

In Virginia, another key presidential battleground state, several new voting laws are going into effect.

Due to bills signed under the previous Republican governor, Virginia implemented a photo ID law and limits on group registration drives. But the state's current Democratic governor, Terry McAuliffe, has moved to restore ex-felons' voting rights. The Virginia Supreme Court is expected to weigh in on the legality of the executive order.

These efforts could cancel each other out, said University of Virginia political scientist Larry Sabato. "Obviously, there is some impact," he said. "But from what I've seen so far, I doubt the new voter ID law will affect the presidential results unless it's a squeaker, and increasingly, I do not believe this one will be a squeaker."

It's also worth noting a somewhat counterintuitive possibility that could pop up in any of the states above: Efforts to restrain access to the polls might produce a backlash, actually driving more minority voters to the polls. But any such impact at this point would be speculative.

Among the states that have expanded voting access, the one that could potentially have the biggest impact on 2016 results is Colorado, a state that has been fiercely contested by presidential candidates for several cycles running.

In 2013 and 2014, the Democratic legislature and a Democratic governor approved Election Day registration and encouraged widespread voting-by-mail, among other provisions. The new system is "definitely more convenient," said Daniel R. Diorio, an elections policy specialist at the Denver-based National Conference of State Legislatures. That could give the Democrats a leg up -- unless it also helps make it easier for less-frequent voters who support Trump to cast their ballots.

There's a caveat, however, for states like Colorado that have moved to mail-in ballots. Political scientists have seen mixed evidence about whether such a move increases turnout overall or whether it just changes the timing or method of turnout -- say, more early voting as opposed to voting on Election Day or more mail instead of in-person voting.

Finally, there are some states that have potential ballot-counting concerns beyond changes in the law.

Arizona hasn't implemented a far-reaching change in its election laws since the last presidential race. But during this year's primary, voters were incensed by long lines, especially in populous Maricopa County, where there was one polling place for every 108,000 voters. The long lines followed the GOP-held legislature's cuts to county election offices.

While Arizona has historically been reliably Republican in presidential elections, the state's expanding Latino population could be energized to vote against Trump, making this a potential opportunity for Democrats.

Georgia is another state that has voted Republican in recent elections but could become competitive in 2016 if Trump's candidacy energizes minority voters. A reduction of the state's early voting period is already in place and a proof-of-citizenship law for voting registration, on hold since 2009, is poised to be in effect for the 2016 general election.

"In terms of real impact, I think the shorter early voting period has a bigger impact than the new voter ID law," said veteran Georgia political journalist Tom Baxter. "In a very close presidential race in Georgia -- which I don't foresee but is possible -- the shorter period could reduce turnout enough to matter."

Two other states that are either a big presidential battleground state this year (New Hampshire) or have several competitive statewide races on this fall's ballot (Indiana) will also be testing out new election rules for the first time in a presidential election. But experts say the new rules are not expected to be sufficiently disruptive in either state.

All this said, of course, it's worth remembering that none of this may matter if the margins of the presidential race and other key contests aren't razor-thin.