Captain America #344 page 42 with Viper Action by Kieron Dwyer and Al Milgrom (1988)

From Captain America #344 - the double-sized finale to the "Don't Tread on Me," a story featuring Viper contaminating the nation's water to turn citizens into reptiles - including Commander-in-Chief, Ronald Reagan! Steve Rogers, garbed as The Captain, makes his way to the White House to slip the mutated President the antidote, but battles him instead. Viper steps in from her hiding spot in the Oval Office to complicate the fight, but she retreats when Secret Service reinforcements arrive.
Great battle page and my first to own that features Steve as The Captain. From August 1988.

Fellow Cap fan? Check out this Cap comic book fan group I started in 2020 which includes several artists as members, including Cap artists like Mike Zeck, John Beatty, Mike Perkins, Tom Morgan, Josef Rubinstein, Bob Sharon and many more! https://www.facebook.com/groups/captainamericacomicbookfans. And if you want to listen to great discussions, reviews and interviews about Cap, you should check out https://captainamericacomicbookfans.com