The GOP primary between Illinois Reps. Don Manzullo and Adam Kinzinger is the most pronounced generational battle of the cycle. The biographies of the 20-year Congressional veteran and 34-year-old freshman reinforce that. So do their fundraising reports.

The contest, which will be decided a week from today, boils down to a proxy battle between the past and the future of the Republican Party. According to recent fundraising, the Members (and former Members) choosing sides in the fight also largely break along generational lines.

Consider this: Dennis Hastert (Ill.), the GOP’s last Speaker, donated to Manzullo while current Speaker John Boehner (Ohio) contributed to Kinzinger. Boehner’s Freedom Project PAC gave $5,000 to Kinzinger at the end of last year.

Hastert, who served 14 years in Congress with Manzullo but never served with Kinzinger, gave his former colleague $5,000 late last month through his Keep Our Mission PAC.

House Majority Leader Eric Cantor (R-Va.) officially backed Kinzinger last week. His Every Republican Is Crucial PAC had already donated $5,000 to Kinzinger in December. Majority Whip Kevin McCarthy (R-Calif.) also donated to the freshman last year.

It’s not surprising that the GOP’s top three leaders would side with one of the party’s “Young Guns” over an entrenched veteran lawmaker, especially given the rise of tea party Republicanism.

Kinzinger’s recent reports to the Federal Election Commission feature a lengthy list of up-and-coming GOP lawmakers.

Among his fellow freshmen who have sent checks from their re-election campaigns or PACs are Reps. Brett Guthrie (Ky.), Trey Gowdy (S.C.), Jaime Herrera Beutler (Wash.), Kevin Yoder (Kan.), Steve Womack (Ark.), Tim Scott (S.C.), Cory Gardner (Colo.), Tom Reed (N.Y.), Scott Rigell (Va.) and Jeff Denham (Calif.).

Other contributors include Reps. Michael Burgess (Texas), Duncan Hunter (Calif.) and Tom Rooney (Fla.) and Energy and Commerce Chairman Fred Upton (Mich.), whose committee Kinzinger serves on.

Far fewer Members have given to Manzullo, who was first elected to the House in 1992. His supporters include Rep. Louie Gohmert (Texas), who gave $2,500 in February, Rep. Lee Terry (Neb.), who sent a $1,000 check from his Big Red PAC on March 5, and Financial Services Chairman Spencer Bachus (Ala.), who has given at least $4,000 through his PAC and campaign committees.

Rep. John Shimkus, who joined Cantor in endorsing Kinzinger last week, gave to both of his Illinois colleagues late last year.

The contest has taken on an increasingly negative tone in its closing weeks as the lawmakers have tried to shine a bright light on the narrow ideological space between them.

Kinzinger’s latest TV ad strikes at the heart of the future-vs.-the-past dichotomy.

“What can Don Manzullo accomplish in the next two years that he couldn’t accomplish in the last 20?” Kinzinger asks in the spot.

An announcer then says Manzullo is “part of the old majority that lost its way on spending,” before calling him the “king of earmarks.”

Manzullo’s ads have sought to portray him as the “true conservative” in the race. One of his recent spots hits Kinzinger for spending “millions on [Minority Leader] Nancy Pelosi’s pet earmark” and an announcer charges that the freshman’s “record isn’t much different than the Democrat he replaced.”

Kinzinger outspent Manzullo $580,000 to $452,000 in the pre-primary period from Jan. 1 to Feb. 29. Both lawmakers had roughly the same amount of cash for the last leg of the race: Manzullo had $334,000 to Kinzinger’s $315,000.