Sessions has been in Congress for almost 20 years and has just become the first sitting senator to endorse the GOP frontrunner, CNN reports. Alabama is set to vote in its Republican primary on Super Tuesday and, though Real Clear Politics shows he’s already in the lead, having the senator’s support could help solidify a Trump win.

Trump began his campaign by announcing that he wants to build a wall between the U.S. and Mexico to keep out “crime” and “rapists,” something that has been a large part of his campaign platform ever since. “We want strong borders. We want the wall,” the businessman said at a campaign rally on Sunday before introducing Sessions as “the expert as far as I’m concerned on borders.” Sessions is well known for his strong views on illegal immigration, and his endorsement of Trump suggests that he has the toughest stance on the issue out of all the candidates.

This comes after former Republican presidential candidate Chris Christie endorsed his former rival on Friday, making this Trump’s second major endorsement in just a few days.