(The Center Square) – President Joe Biden on Thursday set a new target of 200 million Americans being vaccinated by the end of April while also facing questions about the southern U.S. border crisis, the potential to end filibusters in the U.S. Senate and other issues.

At the first news conference of his presidency, held later into his first term than recent presidents, Biden said the U.S. was on target to vaccinate more than 200 million Americans by his 100th day in office.

"I know it's ambitious, twice our initial goal," Biden said. "I believe we can do it."

Biden's initial goal was 100 million Americans vaccinated in his first 100 days.

"We met that goal last week, on Day 58," he said.

On the border crisis, Biden said adults who have crossed into the U.S. illegally should be sent back to their home countries, but he didn't answer a direct question about whether the thousands of children who entered illegally since January would all be sent home.

"They should all be going back," the president said of adults who have been detained at the border, adding that Mexico hasn't accepted many of them.

'We’re in negotiations with Mexico," he said. "That's going to change."

More than 100,000 non-citizens attempted to cross into the U.S. from Mexico last month alone, many of them unaccompanied minors. Since January, more than 11,000 unaccompanied minors have been apprehended crossing the U.S.-Mexican border into Texas. Many of them have been packed into detention facilities, sleeping on concrete floors.

Texas Gov. Greg Abbott has repeatedly criticized Biden over the growing humanitarian crisis at the Mexican border, saying he and Texas officials will deal with the problem if the federal government won't.

"No child should be in" border patrol facilities more than 72 hours, Biden said, adding that's "totally unacceptable."

He said officials are attempting to reach the children's families and either return them home or place them in Health and Human Services facilities for longer-term care.

In an attempt to downplay the crisis, Biden said there often is a surge of illegal border crossings during winter months, when it's cooler in Mexico and Central America, and blamed his predecessor, former President Donald Trump, for "dismantling" the system in place meant to deal with large inflows of illegal immigrants.

He said his administration is in the process of "rebuilding the system to accommodate what is happening today."

On Twitter, Republican U.S. Sen. Lindsay Graham said Biden doesn't have a true grasp of what is going on at the U.S.-Mexico border.

"With all due respect, this press conference is hard to watch. The misinformation being given by President Biden on immigration is stunning," Graham said. "It’s clear he does not have the situational awareness he needs to understand what is going on at the border or how to fix it."

Biden also was asked about the use of the filibuster in the U.S. Senate to block legislation being pushed by Democrats. The Senate is divided evenly, 50-50, between Democrats and Republicans, with Vice President Kamala Harris holding the tiebreaking vote. But 60 votes are needed to break a filibuster.

"It's being abused in a gigantic way," Biden said of the filibuster, adding that he would support efforts to make its use more difficult and suggesting that ending it might become necessary.

"We've amended the filibuster in the past," he said. If that doesn't work, "we'll have to go beyond what I'm talking about."