It wasn't until we got to the 21st century that the party positions had clearly reversed. Today, it's the Republicans in Congress who worry that the sequester is taking too much away from the Defense Department. Most Democrats couldn't care less.
So what's the reason for the flip flop? There isn't any. That's the way sociologies are. They are fads that change through time.
Here is a different way of thinking about John Kennedy: Let's look at him through the prism of ideology.
Throughout the 20th century (and actually for the past three centuries) the primary ideological divide was between individualism and collectivism. On this spectrum, there is no doubt about where Kennedy stood. He was pro-government. Yes he was anti-communist. But when it came to the issue of the individual versus the state, he was pro-state.
Consider this oft repeated quote:
To conservatives, that statement sounds patriotic. To liberals, it sounds illiberal. (The typical liberal campaign sound bite lists as many things as possible that the government will do for you if only the candidate is elected.) One more bit of evidence that Kennedy was a conservative. Right?
Ask not what your country can do for you; ask what you can do for your country.
Here is a different way of looking at it. Think of it as a political philosophy. It's the opposite of the Jeffersonian philosophy. For Jefferson the purpose of government is to protect individual rights so that people can pursue their own happiness. For Kennedy, government (national purpose) is an end in itself and people should serve it rather than pursuing their own happiness.
Once you see that Kennedy believed in big government as an end in itself, everything else falls into place.
On the international front, most people who are pro-government tend to also be pro-war. In fact the primary way government has acquired power — certainly in this country — is by going to war. An aggressive anti-communist foreign policy is consistent with this approach.
Or take the famous Kennedy tax cuts. To conservatives, this proves Kennedy was a supply-sider. And he was. But remember what happens when you are on the wrong side of the Laffer Curve. When tax rates are lowered, government revenues go up. That means government gets bigger. It can spend more money. Do more things.
Casey Mulligan points out that Kennedy was actually rather chintzy when it came to welfare programs. According to Mulligan, Kennedy economic adviser James Tobin worried that if welfare was too generous, families would have an incentive to remain on the dole rather than working and producing.
Sounds just like modern conservatives? Yes, but it's also in the tradition of the father of social insurance, Otto von Bismarck. For Bismarck, the purpose of the welfare state is to tie the self-interest of the individual to the state. He wasn't trying to empower individuals; he was trying to increase the power of the government. And having a lot of people idle doesn't help the state. It drains it of resources.
As for NASA and the goal of putting man on the moon, Kennedy never worried about whether this was taking resources away from the inner city poor to satisfy the curiosity of higher income, well educated people. The space program was one more exciting government venture — another end in itself.
In short, Kennedy wasn't conservative or liberal. He was a believer in big government — at home and abroad; on Earth and in space. It's just that simple.