Former Vice President Joe Biden is pushing back his timeline for announcing a running mate, seeming to signal his campaign has yet to find an acceptable candidate.

Biden told reporters on Tuesday after delivering an address on the coronavirus pandemic that his campaign was still evaluating its options. In late May, he floated the idea of unveiling his running mate by August 1. When pressed if the announcement would meet his initial August timeline, Biden backtracked, claiming his staff was just getting “underway now in the hard vet of going into the deep background checks” required for each of the prospective candidates.

“I can’t guarantee you August 1, but it will be in early August before, several weeks before the convention, I believe,” Biden said.

The remarks come as Biden, who promised to make history by picking a woman as his running mate, has stoked speculation on the topic in recent weeks. First, the presumptive nominee asserted that whomever he chose would have to be “ready to be president on a moment’s notice.” Then, Biden followed up by having allies hint publicly about who was on the shortlist before adding further candidates into consideration at the last minute.

CBS News reported last week that Rep. Karen Bass (D-CA), the chairwoman of the Congressional Black Caucus, was now being vetted for the vice-presidential nomination. Despite not making the initial list, Bass was included after a number of early prospects were either ruled unacceptable by core interests in the Democrat base or withdrew of their own volition.

Part of what has vexed Biden throughout his running mate search is how to balance the Democrat ticket, unite the party after a fractious primary campaign, and, above all, boost his chances of winning in November.

The most notable complication, to date, has been ideological. Biden campaigned for the Democrat nomination as an unabashed moderate, often willing to lambast his progressive rival, Sen. Bernie Sanders (I-VT), and his signature policies, especially Medicare for All. As such, many believe that if Biden were to pick someone outside the party’s progressive wing, he would risk alienating progressives ahead of the general election.

Party unity, however, is not the only issue facing Biden. If he is to have any hopes of ousting President Donald Trump from the White House, he will need to energize one of the Democrat Party’s main constituencies: black voters. Not doing so would all but assure defeat, as some Democrat strategists claim was proved in 2016.

During that election, former Secretary of State Hillary Clinton received 88 percent of the black vote, according to exit polls. Although impressive, the numbers were significantly lower than the 93 percent former President Barack Obama garnered on his way to reelection in 2012.

The drop-off was most noticeable in Michigan, Pennsylvania, and Wisconsin — all states that went for Trump after backing Democrats for nearly three decades prior. For example, data from the Michigan secretary of state’s office indicate Clinton received 75,000 fewer votes in Wayne County — where Detroit is located — than Obama did in 2012. Even though Clinton still won Wayne County by a hefty margin, the decrease prevented her from overcoming Trump’s statewide lead of more than 10,000 votes.

Most political operatives believe that if black turnout was the same in 2016 as it was in 2012, Clinton would have won the presidency, even with Trump’s populist appeal to blue-collar voters. Given such thinking, and surveys showing Biden underperforming among black voters, many Democrats are pushing him to pick a woman of color as his running mate.

Until recently, Biden, himself, appeared to agree. In June, the former vice president’s top allies were hinting that the running mate contest had essentially boiled down to only two candidates: Sen. Kamala Harris (D-CA) and Rep. Val Demings (D-FL). Harris, in particular, was touted as a strong contender because of her fundraising prowess and national profile, both burnished by her own unsuccessful run for the Democrat nomination. Demings, meanwhile, although less well-known, was trumpeted as an effective retail politician with the potential to help Biden carry Florida.

Under normal circumstances, either woman would be considered a shoo-in for the post, even though both are considered more in line with Biden’s political philosophy than that of Sanders. In the wake of the protests over George Floyd’s death, however, the law enforcement backgrounds of both women run the risk of alienating all those demanding an end to racial injustice in the legal system.

This was evidenced in mid-June when Black Lives Matters activists called on Biden to jettison Demings from consideration over her prior career as the police chief of Orlando, Florida. Similarly, Harris, who served as California’s attorney general before ascending to the Senate, has been castigated for once championing tough-on-crime policies, especially when it came to non-violent drug offenses.

Given such developments, Biden’s campaign has taken steps in recent weeks to avoid an in-depth discussion of the running mate search. The former vice president, himself, did not elaborate much on the process while speaking with reporters on Tuesday, apart from mentioning the main “requirement” for a potential running mate is they hold “leadership qualities that lend everyone to believe that they would be ready on day one to be president of the United States of America.”