President Obama is trying to see how much House liberals are willing to compromise on the public option, reports indicate.

Rep. Raul Grijalva (D-Ariz.), chairman of the House Progressive Caucus, told Greg Sargent that Obama used a conference call yesterday to figure out just how serious the coalition was about opposing a bill that has no public option.

“He understands how serious we are about this,” said Grijalva, one of the co-chairs of the Congressional Progressive Caucus, in describing the tone of the conversation. “For many of us this is not a political dance. He got that point.”

Grijalva says Obama asked how far liberals were willing to compromise on the public option, another sign, Grijalva noted, that he grasps that they mean what they say. He added that Obama asked a number of “frank” and “probing” questions, though he declined to say precisely what they were.

Meanwhile, sources give Talking Points Memo a similar account.

A source familiar with the call tells TPM that Obama asked the group to define their red line when they talk about a "robust public option."

NBC reports that Obama reminded the group that they enjoy the security of representing safely Democratic districts.

The big question: Will House progressives support a so-called "trigger" that would implement a public option only if and when the private sector fails to meet certain standards?