One of the thornier issues in American politics is rarely, if ever, discussed at the level of presidential contention.

In many states across the country — including the “Live Free or Die” state of New Hampshire — there is genuine disdain for the federal government policy that requires states to set the minimum age for purchasing and consuming alcohol at 21.

By threatening to withhold highway funds, the feds have forced states that historically have set the drinking age at 18 — respecting the fact that if a young man or woman can be trusted to defend the nation as a member of the military, can be held responsible for his or her debts and can marry and have children, that individual should be trusted to buy a beer and drink it responsibly.

During Wednesday night’s Democratic presidential debate at Dartmouth, a question from a New Hampshire voter put the drinking-age question on the table.

Would any of the candidates favor ending the practice of using federal highway funds to strongarm states into setting higher drinking ages — on the theory that it is wrong to “trust (18 year olds) to make life and death decisions in the military” but not to drink responsibly?

Delaware Senator Joe Biden called the idea “counterproductive.” Translation: “No.”

No one applauded.

Connecticut Senator Chris Dodd replied, “I agree with Joe,” and then somehow veered into a discussion of smoking.

Again, no applause.

New Mexico Governor Bill Richardson proposed a “dual approach,” which sounded good but ended up as another “No.”

No applause.

New York Senator Hillary Clinton, Illinois Senator Barack Obama and former North Carolina Senator John Edwards also indicated that they were in the camp that says an American can die for his or her country but not sip a cocktail.

No applause.

Finally, two candidates, former Alaska Senator Mike Gravel and Ohio Congressman Dennis Kucinich, answered “Yes.”

Gravel said, “Anyone who will fight and die for this country should be able to drink.”

Applause.

Kucinich said, “Of course they should be able to drink at age 18, and they should be able to vote at age 16.”

Applause and a few laughs.

Chances are that few votes will turn on the question of 18-year-old drinking.

But, it should be noted that, in addition to military service, marriage and money, 18 years olds are also trusted with the franchise. And the illogical response of most of the leading candidates may yet drive us all to drink.

Gravel and Kucinich got it right. If you can be trusted to fight and die, and vote, for your country, you can be trusted to buy a beer.