Jeff Sessions says he is running for his old Senate seat to push Congress to act on border security and to stop resisting President Trump’s immigration agenda.

The Alabama Republican is seeking to win a competitive primary and go on to face Democratic Sen. Doug Jones.

“I strongly believe we could have been more effective on immigration, particularly after President Trump got elected,” Sessions said during a half-hour interview with the Washington Examiner near Capitol Hill. “We had the momentum, and it still to me seems [Senate Republicans] have lacked passion and commitment and drive. They need to be pushed. They need to be more aggressive.”

Of his decision to run again at age 72, Sessions added: “I felt like I would be the strongest candidate and sensed that we certainly don’t need to be sending a potted plant to Washington. We need to be sending somebody who’s got backbone.”

Sessions was a senator for 20 years, resigning in 2017 when Trump tapped him to become attorney general. The two had a falling out over Sessions’ decision to recuse himself from authority over the Russia investigation, and he was forced out of the post last November. But Sessions is hopeful they can have a rapprochement and has effusively praised Trump since announcing his campaign earlier this month.

To the extent that Trump has failed to realize his ambitious border security agenda, Sessions blames Republicans in Congress. But Sessions conceded that both Trump and congressional Republicans miscalculated when the issue was shelved after the inauguration in favor of moving to repeal Obamacare and overhaul the tax code.

“It was a missed opportunity, and we can’t miss it when he’s reelected,” Sessions said. “The American people rightly want an end to the illegality,” he said. “If we take it to the American people and force Democrats to vote on these things, people are going to favor the Republican side and not the left-wing, open-borders side.”

Sessions said he supports Trump’s attempts to reach a compromise with congressional Democrats to enshrine into law the Deferred Action for Childhood Arrivals program, which allows some children of illegal immigrants to remain in the U.S. But he said a deal had to be coupled with border security. The issue is in front of the Supreme Court after Trump tried to end the program, created by an Obama executive order, with an order of his own. The issue could be kicked back to lawmakers if the Supreme Court rules in Trump’s favor.

Despite differences over Sessions’ leadership of the Justice Department, he and Trump share a legislative agenda. They see eye to eye on immigration, trade, and foreign policy. Sessions is optimistic that those commonalities, and that he was the first Senate Republican to endorse Trump during the 2016 campaign, will keep Trump from backing one his formidable primary opponents.

Sessions is running against Rep. Bradley Byrne, former Auburn University head football coach Tommy Tuberville, state legislator Arnold Mooney, Alabama Secretary of State John Merrill, and Roy Moore, the ex-judge who lost a 2017 special election to Jones. Trump polls above 90% with Republican voters in Alabama, and Sessions acknowledged the influence Trump could have in the primary.

“I’m taking my case to the people of Alabama, and they will decide who they want as their senator,” Sessions said. “This is not about me trying to have some sort of return to the Senate or some vindication.”