Elected as a Democrat in 1846, Leffler went on to represent Iowa's 2nd congressional district in the U.S. House for additional terms.

Upon the admission of Iowa as a state on December 28, 1846, he was elected as a Democrat to serve as one of two at-large Congressmen for the last two months of the Twenty-ninth Congress.

In 1848, he defeated Whig (and future Republican) candidate Timothy Davis, then served in the Thirty-first Congress.

However, Iowans defied the national trend and voted overwhelmingly for Republican candidates, including Leffler's opponent, Timothy Davis, reversing the outcome of their 1848 race.

[1] This article incorporates public domain material from the Biographical Directory of the United States Congress