The U.S. is close to administering Covid-19 vaccinations at a pace of a million doses a day, suggesting that the Biden administration’s 100-million-doses-in-100-days goal may be a modest aspiration.

In the week Biden was sworn in as president, nearly 983,000 shots a day were administered on average over the seven days ending Friday, according to data from  Bloomberg’s Vaccine Tracker. The most recent three days topped a million doses.

Biden’s goal, essentially, is to not backslide. He made it a theme of his presidential campaign to criticize the prior administration’s handling of the pandemic—including the vaccine rollout that fell far short of then-President Donald Trump’s promises. At the current rate of roughly 1 million shots a day, it would take almost 18 months to vaccinate 80% of the U.S. population.

“God willing, we’re not only going to do 100 million, we’re going to do more than that,” Biden said at the White House on Friday.

Anthony Fauci, Biden’s chief medical adviser, said on Thursday that vaccinating 70% to 85% of the country by the end of the summer would enable a return to normalcy. To do so would mean administering 460 million to 560 million doses, since the current vaccines require a first shot followed by a booster. That’s more than double the rate of Biden’s 100-day goal.

Biden is “taking into account everything that could go right—and also what could go wrong—and he’s making a measured decision about what target we should aim for,” said Vivek Murthy, Biden’s pick for U.S. Surgeon General. “But make no mistake, his goal is not only to meet that, but it’s to exceed that. But we’ve got to pull out the stops.”

Pressed on the 100-million-dose goal on Thursday, White House press secretary Jen Psaki explained the math behind the administration’s thinking. She said that under Trump, 17 million doses had been administered in the first 38 days, for an average rate of less than 500,000 a day, and Biden’s team hoped to double that.

Bloomberg’s data show that the rate has increased substantially since the first weeks of the rollout. A more ambitious plan would be to double the current rate of vaccinations—not the average rate during the early phase of vaccine distribution. That’s what some Republicans have called for.

“America is already on track for 100 million in 100 days,” Steve Scalise, the No. 2 House Republican leader, said on Twitter. “Biden could do 200 million in 100 days. Republicans would support it. Thanks to Trump, he’s already halfway there.”

In the early days of the vaccination campaign, doses were being administered at a trickle. By the time Biden took office, the federal government was making more than 8 million doses a week available through its distribution program, according to allocation figures from the Health and Human Services Department. Shots are going into arms almost as fast.

Those figures include first and second doses of Pfizer Inc. and Moderna Inc.’s vaccines. In total, the U.S. has made available 65 million doses that can be ordered through the end of January and that will ship over the following weeks. Of those, almost 40 million have already been shipped, according to the CDC.

The U.S. spent more than any country in the world to help speed up the development and deployment of vaccines. It secured more than 1 billion doses from six companies before any of the shots had been approved. For all the criticism that has been directed at the early fumbles of the vaccine rollout, the U.S. still leads the world in shots administered and is fifth in the world on per-capita basis.