Former President Jimmy Carter may be the epitome of failed presidents in the eyes of many Republicans.

But the Democrats announced Tuesday that the one-term president will have a prime-time speaking role at their national convention in Charlotte, N.C., in September. Carter won't be there live, however; he'll speak by video.

A news release from the Democratic National Convention Committee quoted the former president:

"Rosalynn and I regret that we will be unable to be at the Democratic Convention this year in Charlotte. However, we remain steadfast in our support for President Obama and the progress he will make in the next four years ..."

The committee said Carter's video would play on Sept. 4, the first night of the three-day convention.

"President Carter is one of the greatest humanitarian leaders of our time and a champion of democracy around the globe," Democratic National Convention Chairman Antonio Villaraigosa said in the release.

As his time in the White House recedes, many Americans appear to view Carter's presidency positively, as indicated by a June Daily Beast/Newsweek poll in which 57 percent of respondents rated him anywhere from "above average" to "one of the best."

But it didn't take long for Republican candidate Mitt Romney's campaign to try to use Carter against Obama. Ryan Williams, a Romney spokesman, said:

"When President Obama picked President Carter to give a primetime address at this year's Democratic Convention, he couldn't have picked a more appropriate surrogate. From high unemployment to a broken deficit pledge, both presidents disappointed the nation by failing to get the economy back on track. From Day One, Mitt Romney will deliver a new direction that emphasizes pro-growth policies — not the failed liberal policies of the past."

For its part, the Republican National Committee on Tuesday also announced additional speakers to the lineup of its four-day convention, which starts Aug. 27 in Tampa, Fla.

Rick Santorum, who was perhaps the most durable challenger to Romney during the Republican primaries, will have a prime-time speaking role, the RNC said.

The inclusion of Santorum, a former U.S. senator from Pennsylvania, is part of the long tradition in both parties to present a unified front at nominating conventions.

While President George W. Bush won't be there, his younger brother Jeb will speak in prime time as well.

Jeb Bush, a former Florida governor, has been an outspoken advocate for his party's outreach to Latino voters. His high profile at the Republican convention could help Romney and the party soften some of the negatives associated with their often hard-line positions on illegal immigration.

Sen. Rand Paul of Kentucky, who won his 2012 race with Tea Party backing, is also scheduled to have a prime-time slot at the GOP convention.

Gov. Mary Fallin of Oklahoma is also scheduled to speak. The first female chief executive of the Sooner State, she joins fellow groundbreaking governors Nikki Haley of South Carolina and Susana Martinez of New Mexico as prime-time convention speakers.

An excerpt from a news release about the speakers announced Tuesday quoted RNC Chairman Reince Priebus:

"I am thrilled to announce Governor Bush, Governor Fallin, Senator Paul and Senator Santorum will address our convention," said Priebus. "As our party unites around Governor Romney, these four great leaders will lend their voices in support of his vision to get America back on track."Copyright 2016 NPR. To see more, visit http://www.npr.org/.