— It may be a small victory, but it was a victory nonetheless for U.S. Sen. David Vitter, R-La., in his stubborn challenge to how the federal government treats Congress under the federal health care law.

The Senate voted 52-46 Friday for Vitter’s proposal to place members of Congress — as well as the president, vice president and Cabinet secretaries — into the individual health insurance market under the Affordable Care Act. Better known as “Obamacare,” the ACA is Democratic President Barack Obama’s signature legislative achievement and the target of unremitting Republican attacks.

The Vitter measure — attached to the Senate’s federal budget plan, passed Friday — is nonbinding and does not require the president’s signature, but it puts the Senate on record in support of his idea. One Democrat sided with Vitter, but three Republicans voted “no.”

But that’s not the only front Vitter has opened in the battle. Nor was Friday the only time he’s encountered pushback from fellow Republicans.

The issue has its roots in 2010, when the health care law was working its way through Congress. A Republican amendment required the federal government to stop offering members of Congress and their staffs the governmentwide Federal Employee Health Benefits Plan — a typical workplace plan, with the employer paying about 75 percent of health coverage premiums — but instead to “make available” only plans marketed through “Obamacare” health insurance exchanges.

For members of Congress and their staffs, that meant their employer — alone among all employers — could not offer them a standard workplace health plan and pick up most of the tab. The health care law bans any employer contribution to the cost of exchange coverage, and all members of Congress and many staffers make more than the maximum income allowed — about $50,000 a year — to qualify for an ACA subsidy.

Enter the federal Office of Personnel Management, which decreed that the government would continue to pay its share of the affected employees’ coverage, provided they purchased it through the District of Columbia’s small-business ACA exchange. Vitter and other critics call that Congress’ “Obamacare” exemption, a sweetheart deal that isn’t offered to any other ACA exchange participants.

In addition, OPM allows members of Congress to declare any or all staff members “unofficial,” keeping them under the FEHBP. In December, Vitter got Senate Republicans to agree to designate all their staff members “official.” But House Republicans rejected a similar proposal. Vitter’s separate legislative efforts to push staff members, too, into the individual exchanges have not yet borne fruit.

Meanwhile, thanks to a lawsuit by a conservative advocacy group, it’s come to light that House and Senate administrators grossly understated the size of the congressional workforce (it’s actually well over 10,000 employees) to qualify as a small business when they enrolled in the D.C. exchange.

Vitter wants to root out who’s responsible for the misrepresentation. The administrators have said they were just following OPM rules — and in the House, they’ve stonewalled Vitter’s request for documents, saying they’re not answerable to the Senate.

Vitter has pressed his case with House Speaker John Boehner, R-Ohio, who directed Vitter’s follow-up request to the same administrator who spurned Vitter in the first place. And the Republican chairman of the House Administration Committee implied Vitter’s quest may be motivated by his interest in scoring political points in his run for governor this year.

Vitter is undeterred. He considers the OPM rule-making an evasion of the law. He also wants to make a case about “Obamacare” in general.

“I think the chefs should have to eat their own cooking,” he said last month. “Usually when you enforce that rule, you get a lot better cooking pretty quickly.”

Gregory Roberts is chief of The Advocate Washington bureau. His email address is groberts@theadvocate.com, and he is on Twitter, @GregRobertsDC. For more coverage of national government and politics, follow The Advocate Politics Blog at http://blogs.theadvocate.com/politicsblog/