House Speaker Paul Ryan just endorsed his former aide Bryan Steil in the race for his own congressional seat. He is preparing to help the Republican front-runner raise enough money to compete in what's turned into a crowded field.

In an expected move Monday, Ryan officially backed Steil for Wisconsin's 1st congressional district, a seat the speaker has held for almost two decades. Ryan is retiring from Congress after the midterm elections.

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Ryan is now planning to help raise money and stump for Steil. The primary will be held on Aug. 14. Steil is competing against five other Republicans. Two Democrats are also in the hunt for the seat.

Ryan's retirement has made the district competitive for the first time in years. Sabato's Crystal Ball calls it a "toss up." Other leading nonpartisan handicappers Cook Political Report and Inside Elections both rate it as a "lean Republican" race.

"Paul is going to do everything he can to help Bryan win this race," a source with direct knowledge of the matter told CNBC on condition of anonymity. Ryan and his team will "be there to support his team with events, fundraisers and whatever other help they need," the source added.

A spokesman for Ryan declined to comment.

Steil's campaign said it was proud to call Ryan one of its supporters.

"This is a Wisconsin based campaign and we are proud to have the backing of Speaker Ryan as we continue to earn the trust and confidence of the voters of Southeastern Wisconsin," a campaign spokesman said in a statement.