Mayor Rahm Emanuel on Wednesday invited “nominations” for Chicago sites that could house Amazon’s second North American headquarters — even as behind-the-scenes competition continued to focus on a handful of downtown options, including the Old Main Post Office and the Michael Reese Hospital site.

Earlier this week, Gov. Bruce Rauner played regional politics on the same day that he and the mayor dispatched a delegation to Seattle to get a first-hand look at HQ1: Amazon’s 8.1 million square-foot, 33 building campus, which houses 40,000 employees.

The governor noted that St. Louis was also competing for Amazon and “we have a major population center in Metro East” with “major strategic transportation advantages” in that Downstate area.

On Wednesday, Emanuel was asked whether Rauner’s remarks about St. Louis were detrimental to the mayor’s own desire to join hands with the state in an “all hands-on-deck, all-resources-to-bear” bid.

“That’s a question for him. I know what I’m thinking about, which is Chicago first. Chicago only…I’m like a laser focus,” Emanuel said, holding his fire.

The mayor was asked whether the “sky was the limit” for an Amazon incentive package or whether there would come a point of no return, even in the competition for the economic development plum of the century.

“You don’t have a company this often….that says, ‘We’re gonna talk about 50,000 jobs.’…This is kind of a unique situation–one that you don’t want to miss,” the mayor said.

The mayor added, “It won’t be kind of the public resources. It will be the strength of the totality of what we’re offering.”

The deadline for the city’s “request-for-nominations” for Chicago sites is Sept. 27. They must be submitted, only by the “property owner or an entity with site control.”

Respondents were encouraged to forge partnerships with “other nominating entities.” But they must also have “demonstrated experience and wherewithal to perform and deliver a project” that meets the demands laid out in Amazon’s RFP, the city said.

They include: 500,000 square feet of “initial space” that can be expanded to up to eight million square feet over the next decade. That’s enough space to house as many as 50,000 employees.

Nominated sites must also provide “direct access” to mass transit, be located within 30 miles of a “population center” and 45 minutes of O’Hare Airport.

The sheer size of the HQ2 project and the must-haves in Amazon’s RFP limit the choices to only a handful of Chicago sites.

The Chicago Sun-Times has zeroed in on six possibilities: the old main Post Office straddling Congress Parkway, perhaps in conjunction with the adjacent Union Station project; two in the North Branch Industrial Corridor; the Michael Reese Hospital site; the 62-acre site in the South Loop once owned by convicted felon Tony Rezko; and a site at Roosevelt and Ogden avenues that is in the Illinois Medical Center District, near the University of Illinois at Chicago, Stroger Hospital, the V.A. Hospital and Rush University Medical Center.

Emanuel has said he doesn’t want to “pick favorites about sites.” That’s up to Amazon.

But he has argued that, unlike other cities, Chicago is not “limited to only one choice.” The city has “a number of sites” that can satisfy Amazon’s demands—either for a “vertical” campus or a “horizontal” one, he said.

That’s why the trip to Seattle was so important.

“They have a vision of their future. … And I want to make sure that all of Chicago lines up to that future,” the mayor said.

The most difficult demand to satisfy is likely to be Amazon’s demand for a “stable and business-friendly environment,” particularly after the marathon state budget stalemate that strained Emanuel’s longtime friendship with Rauner to the breaking point.

Towards that end, sources said there is at least some behind-the-scenes talk of attempting to move an initial Amazon incentive package through the Illinois General Assembly during the fall veto session. But only if the mayor and governor are certain they have the votes to pass it.