Democrats and Republicans likely won't agree on much this election year. But here is one thing on which they should agree and take action: ending the single largest legal disenfranchisement of voters in America.

Those disenfranchised voters are the brave Americans serving overseas in the U.S. military. Under the rules of both parties, they are unable to vote in the selection process for presidential delegates in the many states that hold caucuses to pick those delegates.

There are now more than 200,000 military personnel serving overseas, and more than 1.4 million in the armed forces, who could potentially be required to serve overseas.

Yet those Americans serving overseas, and in many cases risking their lives, were unable to vote in party caucuses in 15 states that held caucuses instead of primaries in 2012, including Arizona, Hawaii, Iowa, Minnesota, Colorado, Nevada, Maine, Utah, Idaho, Kansas, Nebraska, North Dakota, Wyoming, Alaska, Washington, Florida, Missouri and Michigan.

These Americans, if they are Democrats or Republicans and are serving in uniform, can be denied the ability to cast a ballot to select their own party's nominee for commander in chief. How has this been overlooked?

In other areas, great efforts have been made to protect the rights of military voters. But more effort is needed.

For example, federal law requires that local election officials send absentee ballots to Americans living abroad at least 45 days prior to Election Day for general federal elections. That's because of the very long lead time for ballots to get to remote parts of the world, especially war zones such as Afghanistan. Once a soldier at a firebase in Afghanistan or on a submarine in the Pacific receives his ballot, he still has to mail it back.

Because the U.S. Postal Service has an unjustified monopoly on federal programs for the return of military ballots to the U.S, the absolute minimum time required for such mail round-trip is 30 days. Most experts agree that 45 days is the real minimum. That's why federal law was amended in 2009 to add the 45-day requirement for general elections.

Unfortunately that law also gave the Postal Service its monopoly on the return of ballots by international express service. That monopoly should be ended so private services can compete.

But while Americans serving in the military overseas can at least request and receive absentee ballots for a federal election by mail, it is obviously impossible for them to show up at Democratic or Republican Party caucuses in the states that hold caucuses instead of primaries.

With the stroke of a pen putting his signature on a letter to Democratic National Committee Chair Debbie Wasserman Schultz, President Obama could ensure that DNC Rules are changed to guarantee the voting rights of those military voters in future elections.

A Republican Party rule adopted in 2008 requires states to "use every means practicable" to encourage participation by military voters. But the Republican Party needs to do better than that. Republican Party rules can only be changed at a national convention. And that is what they should do, by adopting a new rule that would guarantee voting rights for Republican military voters at the earliest opportunity, which is the Republican National Convention in Tampa.

Regardless of where they are stationed, military voters should be given the same absentee voting rights as they have in a primary or general election.

Would requiring absentee voting for military voters in a state's caucus process involve some change in that process? Yes. Are these reasons to disenfranchise military voters serving overseas? No.

Of course President Obama cannot change Republican Party rules, and the Republican Party cannot change Democratic Party rules. But President Obama can ensure that Democrats change their rules to end the disenfranchisement of those serving in the U.S. military overseas. And the Republican Party can make that same change in August at its convention. It is way past time for that to happen.

If President Obama is so concerned about "voter disenfranchisement," he should show leadership on this vital issue. And Mitt Romney should join him in supporting the enfranchisement of all of our military voters

Hans A. von Spakovsky is a senior legal fellow at The Heritage Foundation.