We've all encountered this in our private lives, people with whom we have agreed with on a huge range of economic and cultural issues are just downright wrong on the war.Actually I don't know any ideological conservatives in real life. At least none that I know of. I do know of many on the net, of course. So it's an interesting question.
They don't trust the government to run the economy, our families, or our schools, but think it is just great for the US to amass the largest military machine owned by any government in the history of the world, for the US and its allies to be the sole nuclear monopolists, for the US to slaughter people in a foreign country who have never done anything to us and spend twice that country’s GDP in doing so.
Tucker surveys a number of explanations for the switch, but he does not really hit on what I think is correct. His explanations are: neoconservative influence, loyalty to the GOP, TV, talk radio, lack of ideology, and nationalism. Each of these, I think, does have some explanatory power, but along with Tucker none seems to be fully sufficient. (Read the piece.)
My thoughts on the matter: in the long run, in politics, there are only two stable ideologies: liberty (private property) and socialism (public property). However, in everyday politics people often box off political domains and take one ideology in some, and the other ideology in others. To the extent that two domains intersect, either ideologically or practically, this may or may not be easy to do. But regardless, people do it all the time.
For example, Americans have boxed off old people from normal society, and decreed that socialism is the proper way to deal with them. Socialized income, medicine, etc. To some extent this conflicts with liberty for others - if the government has the power to tax for social security, it obviously has the power to tax for just about anything. Socialized medicine tends to creep. But largely speaking, old people and their needs can be walled off.
Back to conservatives: in the cold war, foreign policy was an example of a socialist enterprise walled off from the rest of American society. Everyone agreed on a strong defense. Thus, strong taxation came to be accepted by most people - liberals love it anyway for the hope of pulling down the rich; conservatives originally opposed it, but came to grudgingly accept it. But now, massive taxation is now old. Being what they are, conservatives are conserving it.
When the cold war ended, foreign policy as a ideological/political domain became untethered. Spending levels were way too high for the drastically lowered threat. Change was possible. We might have gone back to a more isolationist, lower taxation situation. But there was also the opposite pull: more intervention, higher taxation, invade-the-world. Libertarians know which way to go; our ideology tells us. Conservatives know nothing ideologically; only that whatever is old is probably better than what is new. They have an older history of low spending; true. But they also have a recent history of high spending. So in theory they might have gone either way. But note that taking on new missions for the military can be done right up to the point where spending is about where it was in the cold war. This is the course of minimal change. That has to be the most appealing for a conservative. Over time, this is exactly what has happened. It started right with the first Iraq war.
It was quite clear, in the 90s, that the military industrial complex was thrashing about like a wounded hydra, looking for a raison d'etre. During the 90's, the "solution" was not found, although we did get involved in the Balkans, Columbia, and other places. Some stuck, some didn't. But none really challenged our massive military. Spending was actually getting cut! Oh no! Well, glory be, 9/11. Suddenly Americans actually felt like military spending. And suddenly it is springtime for conservatives: they have found a mission that explains their desire to not change military spending. (And also, I think, all the explanations Tucker considers do come into effect as well.)
Foreign policy, in other words, has hardly realigned at all. For conservatives, the Enemy was the Soviet Union; the Enemy became untethered there for a while, drifted around, and has now settled on "terra": the Muslim world as a whole. Unfortunately, this is having the effect of realigning conservatives on domestic policy: to fight a war on terra we have to cut back on civil liberties. Exactly how much liberty to give up: that's the hot new issue for conservatives. This is, naturally, distressing to any libertarian.
Libertarians argue that we don't need to have an Enemy at all, and thus, don't need to give up any liberty for security. This is directly contrary to the conservative experience of the last 50 years.