Rep. Peter Welch did whatever the online iteration of “putting one’s foot in one’s mouth” is, Tuesday when he apparently forgot that slavery existed in the United States.

The Vermont Democrat was trying to publicize a bill he introduced Tuesday prohibiting government agencies from making their employees work without pay.  The bill would provide immediate backpay to federal workers that have been stiffed during the shutdown.

Simple enough, right?

“Never in the history of this country has it been legal to make people work for free but that’s what’s happening to federal employees. This can never happen again,” Welch tweeted, linking to a story about his bill.

Just a couple hours later, Welch issued the corrective tweet along with his “sincere apologies.”

In Welch’s later tweet, he wrote that there is “nothing worse in the history of our country than the brutal inhumanity of the horrible, relentless, and savage infliction of involuntary servitude — slavery — on millions of people whose freedom was denied.” 

Enslavement of mostly Africans and African-Americans by white colonists was legal in all 13 British colonies that eventually formed the United States in 1776 with the Declaration of Independence.

Slavery was codified in the Constitution, with enslaved blacks counting as three-fifths of a person toward a state’s population total for determining the number of electoral votes and House seats it received.

The institution remained legal in roughly half of all U.S. states, and dominated the contentious American politics of the mid-19th century until the outbreak of the Civil War.

In December of 1865, the 13th Amendment abolishing slavery was ratified.