“It’s the perfect visual validation. Voters can recognize Barack Obama in a nano-second,” said Eric Jaye, a California-based Democratic political consultant. “Obama might as well be on Mt. Rushmore for Democrats. It’s so powerful and instantaneous.”

Most of the spots show footage of Obama lauding the candidates by name in his speeches or on the campaign trail. Others merely include pictures of him by their side. All drive the message that the candidates running the ads are, at least in some measure, approved by a former president who is beloved by the grassroots.

Former vice president Joe Biden was the first to highlight his relationship with Obama by making him the center of a TV ad that ran over the Martin Luther King Jr. holiday weekend. Using audio from a 2017 speech, the ad shows Obama bestowing Biden with the Medal of Freedom, the highest civilian honor in the U.S.

Biden is a “resilient, humble and loyal servant,” Obama says, adding that he’s “nowhere close to finished.”

Billionaire candidates Michael Bloomberg and Tom Steyer have also embraced Obama in an attempt to establish their party bonafides, piecing together soundbites from his speeches that reference them directly or indirectly.

In Bloomberg’s spot, Obama calls him a “leader throughout the country.” Steyer uses footage from Obama's first campaign swing through South Carolina to highlight Edith Childs, who coined his famous "fired up, ready to go" slogan in 2008 and has now endorsed Steyer for president.

Bloomberg has put the most money behind his Obama TV ad — he spent more than $1.2 million in over 70 different markets, according to Advertising Analytics.

Even Warren, who had a cool relationship with the Obama administration, released a TV ad on Tuesday with a similar congratulatory message from the former president. It’s voiced over by audio from a 2010 Rose Garden speech in which Obama commends Warren for her work founding the Consumer Financial Protection Bureau.

“Elizabeth understands what I believe,” Obama says. “That a strong, growing economy begins with a strong middle class.”

It is not unusual for presidential candidates to feature former presidents or prominent political figures in their advertisements as validators. Obama himself, in his 2012 reelection campaign, included audio from a Colin Powell interview on CBS, in which the former four-star general and secretary of state said he would endorse Obama for a second term. Powell holds up Obama’s record on the economy, saying, “I think we oughta keep on the track that we are on.”

Republican candidates in House and Senate races this year have also borrowed from President Trump in their ads. A number of red-state House candidates have used footage from his rallies and pushed platform points that mirror Trump's positions, shoring up support ahead of their own primaries.

Representatives for Obama would not comment on details of the Democratic ads or specify which campaigns talked to Obama before running them. They maintain that the former president’s increased profile on the airwaves has not yet caused any tension between his office and any campaigns.

The former president has remained notably silent this primary season, not making public appearances with any of the Democratic contenders and waiting to endorse before there is a clear frontrunner.

But with less than three weeks until the South Carolina primary, usage of Obama’s likeness in ads could surge as campaigns make a last-ditch effort to increase black support.

“He is enormously well-regarded across the party,” Jaye said. “The timing has more to do with the intensity of the competition than it does the particular affection among African-American voters.”