Sen. Jeff Sessions on Sunday endorsed GOP candidate Donald Trump for president, becoming the first senator to endorse the first-time candidate and billionaire businessman.

The Alabama Republican endorsed Trump at a campaign rally in Mobile.

"The American people are not happy with their government. So some say we should forget it, there is an opportunity this year, Tuesday, the last opportunity we have for the people's voice to be heard. Has the government fixed immigration? Donald Trump will do it," Sessions said. "I am pleased to endorse Donald Trump for the presidency of the United States.”

Among the members of Congress, Session is considered on the toughest on illegal immigration. 

The endorsement is not a total surprise, considering Sessions has appeared on stage before at a Trump rally. However, it will likely be considered a setback for fellow GOP presidential candidate Texas GOP Sen. Ted Cruz, whom Sessions has supported.  

“There is a man I respect that is an expert on the borders and so many things, we want strong borders, we want to the wall ... We are going build that wall, they are going to come into this country, but legally. I think of a great man, who am I talking about? No one knows, kept it a surprise -- Senator Jeff Sessions,” Trump said in introducing the lawmaker.

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Fox News’ Christopher Snyder contributed to this report.