Mayor Rahm Emanuel on Thursday urged South Side residents to “keep your eye on the prize” that is the Obama Presidential Center and not get “tripped up” in talk of road closures and lost park land.

One day after the Obama Foundation offered to bankroll its own garage and the city pledged to widen Lake Shore Drive, Emanuel refused to say why that was necessary, how much the project would cost or where he would find the money.

Nor would the mayor say whether a green roof atop the 450-space garage built on land the city owns on the Midway Plaisance would count as park land.

Instead, the mayor tried to shift the focus to what he called the “forest, not just the individual trees.”

“While we’re gonna talk, correctly, about this roadway vs. expansion of that roadway, this park land vs. that park land, to everybody as the mayor: Keep your eye on the prize because, to quote somebody famous, ‘Yes, we can.’ Let’s just get this done,” Emanuel said.

Emanuel said cost questions are “fair questions.” But he’s not about to provide answers “in the beginning of a process” widely criticized for decisions made behind closed doors.

“Don’t just dismiss the contribution of the parking garage to the community as a whole,” the mayor said. “And don’t dismiss the fact that they’re willing to pay for it. That goes a long way. By doing a green roof, it also goes a long way towards meeting other needs.”

The mayor laid the groundwork for what will almost certainly be a $100 million-plus contribution from Chicago taxpayers by talking about the “tremendous amount of support—both capital as well as operating”–that Abraham Lincoln’s presidential library already receives.

Earlier this week, City Hall and the Obama Foundation took the wraps of an apparent trade-off: The Obama Foundation would build its own, 450-space, above-ground garage on city-owned land on the Midway Plaisance if the land is incorporated into the Obama Presidential Center and the 3-to-4-acre green roof atop the garage is counted as park land.

The timing of the foundation’s offer — on the same day the Chicago Department of Transportation unveiled its proposed road closures and expansions to accommodate the park — suggested it was part of a deal to assuage South Side motorists concerned about losing Cornell Avenue, as it passes through Jackson Park.

Later Thursday, Emanuel reaffirmed his support for a companion, $30 million plan to merge the Jackson Park and South Shore golf courses into a single championship-caliber course.

The golf course merger has stirred controversy because it would require closing Marquette Drive, building a pair of new underpasses, displacing tennis courts and relocating the South Shore Nature Sanctuary to make way for a new 12th hole.

“The mayor is . . . supportive of building a public championship golf course in the heart of the city, which would help drive economic activity and create jobs on the South Side,” deputy press secretary Shannon Breymaier wrote in an email.

“But if the community doesn’t want this project and/or if private funding is not raised, Park District Superintendent Mike Kelly has made it clear that the project will not proceed.”