The homeland security secretary, Janet Napolitano, testified on Tuesday before the Senate Judiciary Committee about the Senate’s bipartisan immigration bill. For hours, in a calm and methodical manner, she flipped each confrontational line of questioning on its head. No, the bill would not loosen security at borders and ports. It would tighten it. The bill would not weaken immigration enforcement, but strengthen it — adding resources and improving the government’s ability to keep unwanted people out and to catch fugitives, identify thieves and terrorists.