During the campaign Landgrebe spent $39,334 and Sprague spent $57,918. On March 23, 1971, the House of Representatives voted on the proposed Twenty-sixth Amendment, which lowered the voting age from twenty-one to eighteen years old, which easily passed with 401 in favor and 19 against. Landgrebe did not participate in the vote on the amendment, but in the past he stated he was against lowering the voting age as the votes of 18 year olds would dilute the votes of older voters. On November 9, 1971, Richard Boehning, the House Majority Leader of the Indiana House of Representatives, announced that he would challenge Landgrebe for the Republican nomination later citing his narrow victory in 1970 and him being the only member of Indiana's Republican delegation to refuse to join the Indiana section of the Committee for the Re-Election of the President. During the primary Landgrebe received the endorsement of fifty-one members of the House of Representatives. However, David W. Dennis was the only member of the Indiana state delegation to endorse him and Charles A. Halleck, who had served in the district before Landgrebe and House Majority and Minority Leader, gave his endorsement to Boehning. He narrowly defeated Boehning with 34,813 votes for 54.20% against his 29,417 votes for 45.80% of the vote. In the general election he easily defeated Purdue University professor Floyd Fithian by riding off of the coattails of Richard Nixon's landslide victory in the 1972 presidential election and in Indiana where Nixon received 66.11% of the vote statewide against George McGovern and received 76,000 more votes than Landgrebe in the second congressional district. Landgrebe gained a reputation in Congress as a "colorful loner" with a unique brand of conservatism. He criticized Lyndon B. Johnson for reducing bombardment of North Vietnam in 1968 and initially supported the United States' invasion of Cambodia ordered by Nixon, but later came out against it and would rather have the United States invade North Vietnam. In 1972, he was arrested during an official visit to the Soviet Union to observe their education facilities due to him distributing Bibles which he did as he was a devout Lutheran. In 1973, he became ill and was treated at Walter Reed National Military Medical Center for ten days during which Nixon visited him. Landgrebe was a stalwart defender of President Nixon throughout the Watergate scandal and during the Nixon impeachment hearings. When the House of Representatives voted to begin the impeachment hearings, 410 voted in favor and Landgrebe was one of the four who voted against.