After weeks of review, the Obama justice department has announced plans to challenge Arizona's controversial new immigration enforcement law in court. The law, which allows Arizona police unprecedented leeway to determine the legal status of state residents, and to impose new criminal penalties on those found to be in the country illegally, is scheduled to go into effect on 29 July.
Obama's liberal supporters have criticised the administration for months for failing to aggressively promote comprehensive immigration reform while, like Arizona, cracking down on illegal aliens. Naturally, they're cheering the president's decision. They're also hoping the lawsuit will help fuel a nationwide commercial boycott of Arizona, which to date has achieved only mixed results.
But Obama's decision could prove divisive, if not explosive.
Six straight national opinion polls have found that a large majority of Americans (60-70%, depending on the poll) support Arizona's harsh new law, even if it might lead to racial profiling. And when asked last week about the justice department's plan to sue Arizona, 56% of Americans said they disagreed with that decision.
And it's not just Republicans. A majority of political independents and a solid third of Democrats disagree also.
In fact, the justice department could well lose its case. An executive order issued by Arizona Gov Jan Brewer has already addressed some of the racial profiling concerns and other potential police abuses that might result from the law's implementation.
And Arizona can plausibly argue that its enforcement crackdown is consistent with federal immigration policy. That could neutralise the argument that it's violating the constitution by "usurping" federal authority.
It's not a slam dunk by any means.
Election year politics, more than anything else, appears to have prompted Obama's decision. His failure to push comprehensive immigration reform, despite repeated promises to do so, is costing him heavily with Latino voters, whose turnout in November could help swing as many as three dozen hotly contested congressional races.
Winning those races could help the Democrats retain control of the House, which is fast slipping from their grasp.
According to a recent Gallup poll, Obama's "favourability" rating among Latinos has declined 12 points since January, while his rating among black and white voters has held steady. But among Spanish-speaking Latinos – those who are most concerned about immigration reform – the president's favourability rating has fallen by a whopping 25 points.
It's not that Latinos are likely to swing to the GOP – at least not yet. But without a cause to rally around, they may simply stay home rather than flock to the polls as they they did for Obama and the Democrats in 2008.
And that's why suing Arizona is potentially so useful. By trumping up the law as "racist" and "anti-Latino", and going on the political offensive, the White House creates a cause that Latinos can rally around. And it puts Obama in the limelight and squarely on their side.
Latinos oppose Arizona's law 3-1. The GOP has largely supported the measure, and is likely to increase that support if Obama sues. Arizona could well become one of the defining issues of the November campaign.
But it's a huge gamble for the White House. Further inflaming public opinion and deepening the polarisation over immigration could turn off independent swing voters who are just as critical as Latinos to the electoral outcome this November.
And it could torpedo last-ditch efforts by Senate Democrats to attract GOP support for a comprehensive reform bill. Senate Republicans are already upset with Obama for ramming health reform down their throats. If he uses Arizona to tar the GOP as "anti-Latino", it will amount to a declaration of war.
But some observers believe the Obama may be be giving up on the GOP and may be prepared to "go it alone" on immigration reform. There are rumours that the White House is reviewing a plan to declare a legalisation programme for the undocumented through a presidential fiat – technically, a special "executive order" – in effect, bypassing the Congress altogether. It would be unprecedented.
Another option being discussed is to try to pass a legalisation plan right after the November elections and before the new Congress gets underway in January. It's a rarely used legislative manoeuver known as a "lame duck" session that allows losing members of the House and Senate to vote on and approve controversial legislation that can't be overturned by their successors.
That the administration is even considering such controversial manoeuvers is a sign of just how high the immigration policy stakes have become, post-Arizona.
And how much of a political firestorm may still lie ahead.