WASHINGTON — White House officials sought valuable primetime air for a rare, impromptu Tuesday night address to tout the accomplishment of signing up more than 7 million people under the Affordable Care Act.

But network officials refused to make the kind of accommodation they did previously for the announcement that Osama Bin Laden had been killed, for instance, and Obama was left instead cutting into the much smaller audiences of Ellen and other daytime shows.

Three sources familiar with the request confirmed the White House asked for the primetime slot in their effort both to emphasize a bright moment following the challenging roll out and, more important, to try to reintroduce the country to a law that remains unpopular. One top White House official referred BuzzFeed to another top official for comment on the conversation with networks, but the second official did not respond to a request for comment.

People familiar with the request declined to reveal which network blocked the primetime address, but broadcast networks have traditionally been much more reluctant than cable networks to provide the White House with evening air time.

Instead of the primetime speaking slot the White House wanted, Obama and Vice President Joe Biden lauded the accomplishment in a less formal Rose Garden address that was alternately celebratory and hard-edged.

"In the end, history is not kind to those who would deny Americans their basic economic security. Nobody remembers well those who stand in the way of America's progress or our people," Obama said.

The White House rarely asks for primetime broadcast TV time for Obama outside the traditional State of the Union address. Indeed, the Oval Office message is one of the traditional venues for presidential communications Obama's team has shunned in favor of digital and nontraditional media tools that don't require the help of established media. But while a primetime address remains a powerful tool available only to the sitting president, networks face a different imperative: protecting their profitable primetime lineup.