Though Democrats are vying fiercely to get onto the stage for the next round of primary debates, most have been slow to RSVP to an invitation that has been extended to all of them - as well as to President Donald Trump. So far, only five Democratic candidates have committed to attend a Presidential Candidate Forum in Sioux City, Iowa, on Aug. 19-20, organized by a group of Native American organizations to spotlight issues such as housing, health care, environmental impact, education, poverty, and missing and murdered indigenous women. That's a mistake: Native American voters might not be numerous, but they are clustered in states that likely will be critical to the outcome of the 2020 presidential election.

Roughly 5 million people identify as American Indians or Alaska Natives. Using 2012 data, the National Congress of American Indians estimated that voter turnout among Natives is 5 to 14 percentage points lower than that of other racial groups, diluting the political power of those voters.

That's particularly disheartening, since Native American voters are concentrated in places where they could make a difference on Election Day. In the 2016 election, Trump won Michigan, a state with more than 100,000 Native American people of voting age, by around 11,000 votes. Arizona, a state Democrats want to capture in 2020, has a voting-age population that is approximately five percent Native American. In 2018, 1.5 percent of eligible voters in Wisconsin were either American Indian or Alaska Native; in 2016, Trump won the state by a single percentage point. North Carolina, a state Barack Obama won in 2008 but which he and Hillary Clinton lost in 2012 and 2016, respectively, is home to the Lumbee Tribe, the largest tribe east of the Mississippi River.

There are unfortunate historic reasons for that gap in voter turnout. Though all of the estimated 300,000 Native Americans were conferred U.S. citizenship in 1924, their right to vote wasn't guaranteed until 1948. Even then, many states raised barriers that limited indigenous suffrage well into the 1970s. And these obstacles to voting haven't gone away: the people erecting them have just gotten more creative.

Repressive voter-identification laws disproportionately affect Native American voters in places such as North Dakota, which enacted a law recently upheld by the Supreme Court that requires voters to show an ID with a physical street address, even though many Native Americans who live on reservations don't have one. Many native communities have reported that distance to the nearest polling place and hours-long waits to vote become significant burdens for voters who want to cast their ballots. And elected officials haven't given Native American voters a good reason to turn out. In Arizona, trust in local government was merely 16 percent among the indigenous people surveyed by the Native American Rights Fund.

Combine these factors with the lack of direct appeal to indigenous communities, and the result is real consequences at the ballot box, especially in elections determined by tiny margins in a few states.

Though votes are important, politicians shouldn't just engage with Native American communities only during election season. Many indigenous communities are the most in need of creative policy solutions to long-running problems. Native Americans have the highest poverty rate of any racial group in the United States and, on some reservations, unemployment exceeds 40 percent.

A few Democratic candidates have recognized these disparities, and are aiming to combat them. Sen. Bernie Sanders, I-Vt., has a platform that would prioritize tribal treaty rights and sexual violence against American Indian and Alaska Native women. In her "Native American Justice" platform, Marianne Williamson calls for returning the Black Hills to the Sioux Nation and halting construction of the Keystone XL pipeline. Sen. Elizabeth Warren, D-Mass., has called for Native Americans to be included in the current reparations discussion. And last month, former housing and urban development secretary Julián Castro put forth a plan to address the disparities in Native American communities, including by focusing on strengthening tribal sovereignty and honoring treaty commitments.

Indigenous communities are pressing politicians to see that native visibility, voices and votes matter. Addressing their concerns should be seen as a civil and moral obligation to presidential candidates, regardless of party. And if Native American voters can play a crucial role in the 2020 election, that might finally force politicians to show up for these long-neglected voters - not just at candidate forums or campaign stops, but throughout every year.

This article was written by Joshua Adams, for The Washington Post.