By the time the 1964 presidential campaign came around, the Republican Party was already in bad shape. They lost the presidency in 1960, Democrats controlled Congress with huge majorities. And even added to those majorities in 1962 and the classical conservative base of the Republican Party, felt the needed to fight back and take control of the party as they did in 1964. After what they saw as moderate leadership from the Eisenhower Administration in the 1950s. And they saw Vice President Richard Nixon as a moderate presidential candidate.
This is how Senator Barry Goldwater became the 1964 Republican presidential nominee and one reason why Dick Nixon didn't run for president in 1964 and why Governor Nelson Rockefeller was treated so badly at the 1964 Republican Convention. Because a new political faction was in charge of the GOP. That believed the Kennedy-Johnson Administration was moving the Federal Government too far away from federalism. And growing the Federal Government too rapidly with the Great Society and they felt the need to step up and nominate someone who they saw as a Classical Conservative and a Constitutional Conservative. Who would bring the Federal Government back in line with the U.S. Constitution.
This is how exactly Senator Goldwater ran his presidential campaign and even had some success in the South. And won some Southern states that the Democratic Party use to own. 1964 was the start of a movement in American politics, that started to move the South from being a purely Democratic region and made it more competitive for Republican candidates. Which is one reason how Dick Nixon was elected President in 1968. And got reelected in a landslide in 1972 and how the Republican Party won 5-6 presidential elections from 1968-88. Four of those elections that they won were by landslides.
The Republican Party paid a heavy price for Senator Goldwater's landslide lost in 1964, but for only two years. From 1965-67 where the Democratic Party had the presidency and huge majority's in Congress, but it was a short two years, because by 1966, President Johnson was starting to become unpopular. And Congressional Republicans picked up 47 seats in the House and four in the Senate. Republicans were still in the minority in both chambers of Congress, but back in the ballpark, with a shot at making Congress competitive.
Because in 1968 Republicans picked up five more seats in the House to give them 192 and seven in the Senate to give them 43. So the democrats no longer had such huge majorities in Congress and be able to over run the Minority Party. Because the Republican Party now had new states and districts that were put in play for them. In some ways the 1964 general elections was a great defeat for the Republican Party.