President Obama on Tuesday will hail the launch of Obamacare's health exchanges, looking to rally public support behind a law that will define his legacy -- for better or worse.

Obama's health appeal comes just hours after the federal government shut down for the first time in 17 years after Republicans tried to link measures to defund or delay the healthcare reforms to a funding resolution.

The president will speak from the Rose Garden at 12:25 p.m. and is then slated to hold an Oval Office meeting Tuesday afternoon with Americans he says will benefit from being able to shop online for competing insurance plans.

The president’s message Tuesday: Obamacare will go ahead as planned and Republicans are to blame for shuttering parts of the federal government.

“The Republican strategy to force a government shutdown that will hurt the economy simply because they’re obsessed with sabotaging Obamacare remains deeply unpopular,” a White House official said, previewing the administration’s health care focus on Tuesday and beyond.

However, the administration has made a series of miscalculations about Obamacare’s readiness.

The White House was forced to delay the mandate requiring employers to provide their workers with health insurance or pay a fine and the cap on out-of-pocket expenses for medical costs.

The infrastructure needed to facilitate the most comprehensive overhaul to the health care system since Medicare was created in 1965 isn’t fully ready, either.

For example, small businesses will not be able to sign up Tuesday for the exchanges online as planned. They can’t do so for another month, meaning they’ll need to fax information or use traditional mail to enroll workers in Obamacare.

The array of setbacks have stoked GOP charges that Obama’s health blueprint is not ready for prime time, a narrative that has been a central theme in the party’s government-shutdown fight.

“The House has made its position clear: Keep the government running and ensure basic fairness for all Americans under ObamaCare,” Speaker John Boehner, R-Ohio, said. “Unfortunately, Senate Democrats chose to shut down the government rather than discuss or even recognize ObamaCare’s failures.”

In addition to the president’s Oval Office event, Obama administration officials are conducting a media blitz to tout the health law Tuesday.

Vice President Joe Biden will make an appeal to young Americans that will air on hundreds of college radio stations, and first lady Michelle Obama is promoting the law to women in an online editorial.

This story was posted at 6 a.m. and has been updated.