District attorney

Miller served as an assistant district attorney of Niagara County, New York from 1946 to 1948.^[6] Governor Thomas E. Dewey appointed Miller to fill a vacancy as district attorney in January 1948, and Miller won election to a full term in November.^[6] He served until resigning in January 1951 as he prepared to assume his seat in Congress.^[8]

Congressman

In August 1950, Miller won the Republican nomination in New York's 42nd Congressional district after defeating Melvin L. Payne and James W. Heary in a primary.^[9] He won the general election in November by defeating the Democratic nominee, Mary Louise Nice.^[10]

After redistricting placed Miller in New York's 40th Congressional District, he was easily reelected every two years from 1952 to 1962.^[11] He rose through seniority to become the second-ranking Republican on the Judiciary Committee, and received credit for two major pieces of legislation.^[12] The first was a compromise on the development of Niagara Falls hydroelectric power, and the second was a law authorizing construction of a new Lake Erie‐Lake Ontario canal east of the Niagara River.^[7][13] Miller voted in favor of the Civil Rights Acts of 1957,^[14] 1960,^[15] and 1964,^[16] as well as the 24th Amendment to the U.S. Constitution.^[17]

Miller became influential with respect to the internal workings of the House.^[7] In 1959, he took part in the Republican caucus' action to replace Minority Leader (and former Speaker) Joseph W. Martin Jr. with Charles Halleck.^[7] Republicans had lost House seats in the 1958 election, and decided to replace the moderate Martin with the more conservative Halleck.^[7] In 1960, Miller won election as head of the National Republican Congressional Committee.^[6] In the November election, the party gained 22 House seats, an achievement that was notable because it occurred as Republicans were losing the presidential election.^[6]

Republican National Committee

Miller's success with the 1960 House elections led to his selection as head of the Republican National Committee.^[7] He served from 1961 to 1964, and advocated for the party to become more conservative, including tacitly supporting Goldwater for the 1964 presidential nomination.^[7]

As chairman, Miller oversaw the party's efforts during the 1962 Congressional elections.^[18] Though Republicans lost five seats in the Senate, they gained four in the House.^[18] In addition, Democratic candidates in several races throughout the South experienced tougher than expected races, indicating that the domination the Democrats had enjoyed regionally since the Civil War was in peril.^[18] These included the moderate-to-liberal Senator J. Lister Hill of Alabama, who defeated business Republican businessman James D. Martin by just 50.9 percent to 49.1.^[19] Martin's strong showing demonstrated his viability as a candidate, and in 1964 he was elected to the U.S. House.^[20]

In the early 1960s, leading Republicans including Miller and Senator Barry Goldwater began advocating for a plan they called the Southern Strategy, an effort to make Republican gains in the Solid South, which had been pro-Democratic since the American Civil War.^[21][22] Under the Southern Strategy, Republicans would continue an earlier effort to make inroads in the South, Operation Dixie, by ending attempts to appeal to African American voters in the Northern states, and instead appeal to white conservative voters in the South.^[23] As documented by reporters and columnists including Joseph Alsop and Arthur Krock, on the surface the Southern Strategy would appeal to white voters in the South by advocating against the New Frontier programs of President John F. Kennedy and in favor of a smaller federal government and states' rights, while less publicly arguing against the Civil Rights movement and in favor of continued racial segregation.^{[22][24][25][26]}

Miller concurred with Goldwater, and backed the Southern Strategy, including holding private meetings of the RNC and other key Republican leaders in late 1962 and early 1963 so they could decide whether to implement it.^[27] Overruling the moderate and liberal wings of the party, its leadership decided to pursue the Southern Strategy for the 1964 elections and beyond.^[28]

Vice presidential candidate

Miller speaking in Tallahassee in 1964.

After winning the Republican presidential nomination, Goldwater chose Miller to be his running mate.^[6] In Goldwater's telling, he picked Miller because "he drives Johnson nuts" with his Republican activism.^[29] But by some other accounts, Johnson "was barely aware of Miller's existence."^[29] Miller's Eastern roots and Catholic faith balanced the ticket in some ways, but ideologically he was conservative like Goldwater.^[29] His relative obscurity—"he was better known for snipes at President Kennedy than for anything else"—gave birth to the refrain "Here's a riddle, it's a killer / Who the hell is William Miller?"^[29]

In the general election, incumbent Lyndon Johnson won a landslide victory. The Goldwater/Miller ticket carried only six states - Goldwater's home state of Arizona, plus Louisiana, Alabama, Mississippi, Georgia, and South Carolina.^[30] Despite the defeat, the ticket's inroads into the previously Solid South were seen as an indication that the Southern Strategy was viable, and Republicans continued to pursue it in subsequent campaigns.^[28]