Congressional Democrats are trying to build support for an effort to bar gun purchases by terror suspects, hoping to take advantage of the same public anxieties about security that gave Republicans a ringing House victory. The Democratic push seems likely to fall victim to opposition from the National Rifle Association and congressional gun-rights backers, chiefly Republicans, who have smothered firearms curbs for years. If the Republicans who control Congress block votes on the proposal, Democrats hope to profit politically by winning sympathy from angry voters. ...