The argument in Crawford v. Marion County Election Board is about the constitutionality of Indiana's new voter ID law, the most restrictive documentation law in the country.  If it is upheld, then Indiana voters will be required to show a government-issued photo ID with an expiration date or their votes won't count.  That could shut out many Hoosiers; according to a recent University of Washington study, thirteen percent of registered voters in Indiana don't have such IDs.

But that's not all.  The decision in this case will reverberate far beyond Indiana.  For several years now, more than half of the states have seen heated legislative battles over onerous voter ID bills.  A decision to uphold Indiana's law would bolster efforts across the country to enact new ID restrictions.  

If that happens, then millions of eligible voters could be blocked this November.  Studies show that roughly twenty one million Americans don't have government-issued photo IDs.  The voters blocked by photo ID requirements are not evenly spread.  Senior citizens, young people, people with low incomes, and people of color are far less likely than other citizens to have the kinds of IDs required by Indiana's law.  For some groups, the effects would be devastating.  A 2005 study found that 78% of African-American men aged 18-24 in Wisconsin don't have driver's licenses.

No matter what the breakdown, the Supreme Court's decision will affect whose votes will and whose votes won't count.  That could make a big difference in November's elections.  Restrictive ID requirements like Indiana's could, for example, quell the upsurge in youth participation that has helped shaped the primaries so far.  

But even that's not all.  What's at stake in this case is much more than voter ID.  What's at stake is the future and strength of the right to vote.  Here's why.

To decide this case, the Supreme Court will have to clarify the legal standards for determining when it is OK and when it is not OK for a state to place direct obstacles between eligible citizens and the ballot box.  In doing so, it will likely set the constitutional ground rules for deciding all cases challenging election rules that suppress votes--including sweeping purges of the voter rolls, restrictions on voter registration, and provisional ballot counting rules.  

The broad contours of the legal framework are clear: because the right to vote is at stake, states are required to justify any burden it places on voters.  The greater the burden, the more compelling a justification it must have, and the more closely the law must be narrowly tailored to address the problem.

What specifically does a state have to show to justify hurdles that thwart eligible voters?  If Indiana has its way, not much.

Indiana claims that its law will help prevent voter fraud.  But photo ID does not stop vote-buying, ballot tampering, absentee ballot fraud, or even voting by non-citizens.  All it prevents is something that almost never happens--voting in the name of another registered voter at the polls.  Indiana concedes that there has never been a proven incident of impersonation fraud in the state.  In fact, the law's supporters did not cite a single proven incident of this kind of fraud anywhere in the country.  Impersonation fraud is extraordinarily rare because it is irrational; you risk a lot ($10,000 and 5 years in prison) and stand to gain only one marginal vote.

Even though it has no evidence of the supposed problem its law targets, Indiana claims that it needs none.  Worse, it says that its law should be upheld because it allays fears of impersonation fraud, even if those fears are irrational.

If the Court accepts those arguments, then just about any vote suppression measure would be protected so long as officials raised the fear of fraud.  That would seriously water down the right to vote.  

And the real-world ramifications would be huge.  The fear of voter fraud could be--and recently has been--used to justify a broad range of efforts to manipulate the rules of elections and harm voters.  

The right to vote should be worth more than that.  However the Court rules, it should insist that an eligible citizen's ability to vote cannot be thwarted without a good reason, based in fact.  The Justices should also make sure that any burden placed on voters is no greater than absolutely necessary so that we can live in a fully functioning democracy where all eligible voters are actually allowed to vote.

Wendy Weiser is the Deputy Director of the Democracy Program at the Brennan Center for Justice.