As of 24 hours ago -- and certainly as of 72 hours ago -- the White House's plan was to use Tuesday's speech in Las Vegas to unveil its immigration-reform proposal.

(Kathy Willens - AP)

The proposal was to be significantly more liberal, and vastly more specific, than the framework that the Senate's Gang of 8 unveiled on Monday. In particular, it was expected to have a cleaner, faster path to citizenship, with fewer border-enforcement triggers standing in the way. It was also expected to address some issues the Senate group didn't touch, most notably with a provision saying that same-sex partners would be treated as traditional spouses under the law.

But sometime in the last 24 hours, the plan changed, and the expectation now is that the president's speech will shy away from specifics, and the White House will no longer release a detailed proposal. Instead, the speech will be used to make a general argument for immigration reform, reiterate the president's principles and bottom lines, and embrace the work of the Gang of 8:

This has caused a bit of confusion among activists. "They were clearly gearing up to be aggressive, and it feels like they’re stepping back," says Frank Sharry, director of the pro-immigration group, America's Voice.

The White House was -- and is -- caught between two competing imperatives on immigration reform, as they are on most all major legislative initiatives. On the one hand, they want, and are expected to, "provide leadership." That means everything from helping to guide the construction of the bill to making the public case for it. On the other hand, they know their involvement in the legislation could polarize it, giving Republicans a reason or, depending on your perspective, an excuse to vote against something they might otherwise have supported.

Leaning too far in either direction carries risks. If the White House hangs too far back from the process, the bill could evolve in a direction they don't like. Details of the Senate compromise are already causing some heartburn among immigration reformers, not to mention among White House policy experts. If it gets further watered-down in the House, it could become unacceptable, and the White House will be faced with the unpalatable choice of vetoing the only immigration-reform proposal that can pass or signing a bill they don't like.

But stepping too far into the process carries its own problems. Republicans are wavering on whether to support immigration reform, but they're firmly decided on whether they support Obama. If immigration reform becomes associated with Obama, it could mean Republicans abandon it. As hard as it is for Sen. Marco Rubio (R-FL) to make the case for a path to citizenship to Rush Limbaugh, it's even harder for him to make a case for Obama's path to citizenship for Rush Limbaugh.

For their part, a number of key Senate Democratic aides I spoke to were pleased to see the White House backing off, at least for now. There were a bunch of reasons for them to want to do a bill or roll out a blueprint," one told me, "most of which became moot after the Senate rollout yesterday."

If, as expected, the White House stays vague Friday, it allows them to chart something of a middle path. At this point, everyone in Washington knows that the Obama administration has a fully-realized immigration plan that pro-immigrant groups love. But they'll also know that the White House is giving the Gang of 8 a chance to succeed first.

The choice that leaves Republicans with is this: Stick with the Gang of 8's compromise and pass an immigration-reform proposal that Republicans can live with, and even take some credit for. Or kill it by demanding concessions beyond the point where Democrats can live with the policy, and then watch the White House bring out their proposal, which Republicans will inevitably hate and oppose, and then get blamed by the Latino community for killing immigration reform -- again.

Update: I'm getting conflicting reactions to this post. Hill staffers and members of the advocacy community feel strongly that the White House's strategy shifted in the last day or two. The White House doesn't. They say their speech today, and the document they plan to release, haven't changed except to applaud the work of the Senate's Gang of 8. For reasons they don't fully understand, Washington became convinced in recent days that the administration was going to get extremely, granularly specific, when that was never the plan.

The document they'll release today will closely track their May 2011 paper detailing the administration's principles for immigration reform. That paper, which weighs in at 29 pages, is far more specific than what the Senate group released, but isn't at the granular level of detail required for actual legislation. Today's documents will likely also be more specific than what we saw from the Senate but not so specific that it serves as a detailed, alternative plan.