Only the federal government has the authority to set and enforce immigration policy. So President Barack Obama had little choice but to sue Arizona to block its constitutionally questionable foray into immigration enforcement. Tuesday's suit challenges Arizona on the question of federalism, without delving into whether the new law will lead to discrimination against Hispanics. In many ways, it's a warning to other states that Washington intends to defend its turf.

But with authority comes responsibility. Washington has failed miserably on immigration, inviting an unworkable array of state and local actions. Officials must replace the broken system with one that is effective and enforceable. That includes tighter border security and tougher policing of employers. It means remaking the legal immigration system, allowing more temporary workers, and ensuring that students and tourists leave when their visas expire. And it has to include steps toward legalization for the 12 million people who are here illegally.

With an election looming, reform is unlikely before November. In the interim, beefing up security on the Southern border is the right course. An additional 1,200 National Guard troops were sent there in May. An unmanned, drone aircraft was dispatched in June to enhance surveillance and combat crime along the border. And Obama has requested an additional $500 million for more Border Patrol officers and drones.

Arizona's law and Washington's lawsuit are sideshows. The main event is a comprehensive overhaul of the nation's immigration system. hN