Seven weeks ago, President Joe Biden laid out a lofty goal to vaccinate 70% of all American adults by July Fourth.

The White House now acknowledges it will fall a little short of that target.

Administration officials attribute their miscalculation to a combination of factors.

They include the lessened sense of urgency that followed early success in the vaccination campaign as well as a decision to reach higher than a play-it-safe lower goal.

They also encountered unexpectedly strong resistance among some Americans to getting a shot — especially among young adults.

During a briefing by the White House COVID-19 response team on Tuesday, team coordinator Jeff Zients defended his team's work by noting that pointing to the fact that 70% of Americans 30 and older have been vaccinated and adding that the administration is on track to vaccinate 70% of Americans 27 and older by July 4.

He added that he expected the U.S. would reach the 70% threshold a "few weeks" after July 4.

"We have built an unparalleled, first-of-its-kind nationwide vaccination program," Zients added. "We want every American in every community to be free from fear of the virus...we're not stopping at 70%, and we're not stopping on July 4."

President Joe Biden will continue to push for vaccinations Thursday when he visits a mobile vaccination clinic in North Carolina. There, he'll deliver remarks and urge Americans to roll up their sleeves and get a shot.