A spokeswoman for Mr. Abbott did not respond to calls and emails seeking comment. But Elena Marks, the president and chief executive of the Episcopal Health Foundation in Houston, noted that Mr. Abbott had shown an interest in “how the state might access the Medicaid expansion funds in a way that meets Texas’ needs.” The Houston Chronicle reported last month that Mr. Abbott had privately asked about Utah’s plan to use Medicaid expansion dollars to buy commercial coverage for low-income adults.

“It seems to me that the entire conversation around the A.C.A. has moved away from the hyperbolic, politicized and ideological and toward the pragmatic,” said Ms. Marks, who supports the law.

About five million middle-income people in more than 30 states receive subsidies to buy health insurance through the federal exchange. Without those subsidies, many would not be able to afford it. And without those people in the insurance markets, prices would probably rise for everyone else.

In a new study, the RAND Corporation found that eliminating subsidies for people in the 34 states that use the federal exchange would reduce the number of the insured by 9.6 million.

“I suspect what’s going on is that Republican states realize what a disaster this would be for their insurance markets,” said Timothy S. Jost, a health law expert at Washington and Lee University in Virginia who supports the Affordable Care Act.

No amicus briefs have been filed in support of the government; they are due on Jan. 28.

Most of the amicus briefs supporting the plaintiffs were submitted by conservative organizations and scholars. But 19 Republican state legislators in Tennessee and two in Ohio joined the Galen Institute, a conservative research group, in filing a brief. And four Republican state legislators in Virginia filed a brief with several groups.