The gun control measures a tearful President Barack Obama announced Tuesday would not have prevented the slaughters of 20 first-graders at Sandy Hook Elementary School in Newtown, Connecticut, or 14 county workers at a holiday party in San Bernardino, California.

Obama’s executive action expands mandatory background checks to gun shows, flea markets and online sales, adds more than 230 examiners and staff to help process them and calls on states to submit accurate and updated criminal history data.

Those measures are seen as crucial to stemming gun suicides — the cause of two-thirds of gun deaths — by blocking immediate access to weapons. But, an Associated Press review shows, they would have had no impact in keeping weapons from the hands of suspects in several of the deadliest recent mass shootings that have spurred calls for tighter gun control.

The shooters at Sandy Hook and San Bernardino used weapons bought by others, shielding them from background checks. In other cases, the shooters legally bought guns.

In Aurora, Colorado, and at the Navy Yard in Washington, D.C., men undergoing mental health treatment were cleared to buy weapons because federal background checks looked to criminal histories and court-ordered commitments for signs of mental illness. The Obama administration is making changes in that realm by seeking to plug certain Social Security Administration data into the background check system and by helping states report more information about people barred from gun possession for mental health reasons.

The suspect in a shooting at a church in Charleston, South Carolina, should have been flagged at the time, but errors and delays cleared the way for his purchase.

Though the moves probably wouldn’t have prevented recent mass shootings, Obama rejected the idea that undermines the changes.

“We maybe can’t save everybody, but we could save some,” Obama said.