It wasn't so long ago that Charles Prijatelj, the superintendent of the Altoona Area School District, was receiving up to 150 applications for elementary school teacher job openings.

In recent years, however, the number of applicants for each opening at his 7,400-student district in central Pennsylvania has dwindled to as little as three or four.

“There just aren't enough teachers. There isn't a big pool to pull from. Retirements are through the roof and people are leaving the profession even more than they were due to all the havoc from Covid,” Prijatelj told NBC News. “It's dire."

The decline Prijatelj has seen in his district mirrors a national trend, according to federal data and analysis of that data. And as President Joe Biden pitches universal preschool and free community college as part of his plans to overhaul a coronavirus-ravaged economy, education experts see teachers as the linchpin. The $9 billion that Biden's American Families Plan would set aside to address the country's increasingly acute shortage — one that was worsened, though not created by, the pandemic — represents a critical investment for the White House to make good on many other parts of his domestic agenda, these experts said.