Retiring Alabama U.S. Sen. Richard Shelby “did his best to hold back SpaceX,” Elon Musk said on Twitter today.

Musk’s shot came shortly after Shelby’s retirement on the day Shelby’s successor and former aide, Katie Britt, is sworn in to take Shelby’s seat in the U.S. Senate.

Musk’s then-fledgling rocket company competed with so-called “legacy space” companies like Boeing and Northrop Grumman for space contracts during the presidency of former President Barack Obama.

Those companies and others had large operations in Alabama close to NASA’s Marshall Space Flight Center in Huntsville.

Boeing designed and built the rocket that took the Orion capsule beyond the moon late last year, and Marshall led the development.

The “commercial space” move to develop a backup, lower-cost rockets to carry Americans into space came during the administration of former President Barack Obama. Musk’s company was a leading part of that effort and his rockets and capsules support the International Space Station today.

Shelby was a senior member of the powerful Senate Appropriations Committee during SpaceX’s early development and chaired the committee from 2018 until 2021.

Musk in 2010 told AL.com he didn’t “understand what (Shelby’s) beef is” over a national space plan.

Shelby at the time called Obama’s plan “a faith-based initiative” and “a welfare program for the commercial space industry … where the taxpayer subsidizes billionaires to build rockets that NASA hopes will one day allow millionaires, and our own astronauts, to travel in space.”

“I don’t really understand why Sen. Shelby is so opposed to commercial crew,” Musk said in 2010, “given that Atlas and Delta are right there in Alabama, because no one’s going to be a bigger winner in commercial crew than United Launch Alliance.”