Tom Mann, the Brookings Institution's resident wise man on domestic affairs, has been advising reporters that they can learn more about the next election by focusing on Capitol Hill than by chasing presidential candidates through the early laps on the campaign trail. Last week's gun control battle in the House of Representatives proves his point.

The Senate-passed bill designed to close a loophole in existing law that permits people to purchase weapons at gun shows without background checks was defeated in the House. Most Democrats and some Republicans voted it down after Rep. John Dingell, a veteran Michigan Democrat and former National Rifle Association board member, attached an amendment reducing the waiting period for such purchases to 24 hours -- a change most Democrats said would make the law a sham.

President Clinton and both candidates for the 2000 Democratic nomination, Vice President Al Gore and former New Jersey senator Bill Bradley, roasted the Republican Congress for knuckling under to the NRA and failing to respond to the recent wave of school shootings. They vowed to make guns an issue in the next election.

This is no empty threat. The Columbine High School shootings set off a bigger wave of public revulsion than anything else that has happened this year. On my recent travels, I've heard much more conversation -- and concern -- about school violence than about Kosovo atrocities or the Monica scandals. Columbine hit home with every parent who sends children off to school.

Republican congressional leaders argue they were not to blame for last week's fiasco. Democrats were spoilsports, say House Speaker Dennis Hastert and Majority Whip Tom DeLay. Rather than accept a legislative compromise, they "picked up their marbles and went home."

The argument has some merit. Other provisions in the bill offered some additional protections against misuse of guns, and a House-Senate conference likely would have strengthened them. But there were sound political reasons why the Democrats preferred to have an issue, rather than a watered-down bill.

When the Dingell amendment passed, 218 to 211, all but 47 Republicans voted in favor of it and all but 45 Democrats, against. But it is not just the overall numbers that point to the Republicans' vulnerability on this issue. It's where the votes came from. Rural congressmen from Southern and Western states have an easy time voting for guns; urban members from the Northeast have an equally easy time voting against them.

But the key battlegrounds for both presidential elections and control of the House are the suburban districts. House Democratic leader Dick Gephardt says some polls show "90 percent of suburban women with children favor stronger gun-safety measures." New Jersey, probably the most suburban of all the major states, saw 10 of its 12 representatives vote against Dingell, including four of the six Republicans. One of them, Rep. Marge Roukema, led the debate against the Dingell amendment, declaring, "this issue is about law and order and keeping criminals from getting guns."

California -- the biggest prize in any election -- offers another case in point. Only one of the 28 Democrats supported Dingell, while one-third of the 24 Republicans broke ranks to oppose him. Among those eight are the occupants of the most competitive Republican-held districts in the state.

To be sure, in some major states, such as Pennsylvania, the NRA has sufficient support to make it prudent for four of 11 Democrats to join all but one of the 10 Republicans on Dingell's side. The all-Democratic West Virginia delegation also voted for Dingell and the NRA.

But the states that are likely to be the most closely contested in the presidential race -- states where suburban areas are the key -- voted against the NRA position. Suburban Republicans Henry Hyde and John Edward Porter crossed over to cause a 10-10 split in the Illinois delegation. Florida voted 14 to 9 against Dingell, with half those 14 votes coming from Republicans. It is no coincidence that Florida voters last November approved giving each county authority to require criminal record checks for gun purchasers by more than a 2 to 1 margin.

In conservative Virginia, three suburban Republicans helped form a 5-4 split in the delegation against the NRA. One of those Republicans was Rep. Tom Davis, the chairman of the National Republican Congressional Committee, who preaches constantly that the GOP's shaky majority depends on holding or improving its position in the suburbs.

Of course, the Texas delegation voted overwhelmingly for guns, with eight Democrats joining every single Republican in supporting Dingell. Gov. George W. Bush can rightly claim he reflected the sentiment in his state when he signed a bill last week barring Texas cities from suing gun manufacturers for the damage and destruction these weapons can cause. Whether it was a wise move for a presidential candidate is another question.