Call it the law of unintended consequences. When you fix one thing, it messes up other things.

If the Democrats win the election this year, and are able to enact a health care plan that extends adequate coverage to all Americans, the loser could be the Army. Getting enough people to enlist could become a major problem for the next president.

Senator John McCain, the presumptive Republican candidate, has already pointed out that Senator Barack Obama, the likely Democratic candidate, never served in the military. It remains to be seen how potent that will be as an issue, given the fact that the last four presidential elections have been won by the candidate with the less impressive military resume.

But there is something else that distinguishes Mr. Obama from all recent candidates for the presidency. He would be the first presidential nominee to come of age after the draft was abolished in the administration of Richard M. Nixon. He never had to decide how to deal with the draft, and legally was under no more pressure to enlist than he was to go to medical school or become a bus driver. Joining the military was a career option like any other.

And that has made it harder to put the Army together. Government polls show that the proportion of young people who think they might enlist is roughly half what it was in the late 1980s. The military has responded with more recruiters and higher cash enlistment bonuses, and has met its goals. A significant factor for many recruits, it turns out, is the military’s generous health benefits for dependants.