She laid out three conditions. She wanted her colleagues to pass two separate bills that would shore up insurance markets for people who weren’t covered through their job. And she wanted congressional leaders to promise to undo the Medicare cuts automatically triggered by the deficit increase from the tax cut.

Her colleagues assured her they would pass the bills she wanted — not immediately but soon after the tax bill had passed. Collins decided that was good enough, and on Dec. 2, she became one of 51 yes votes on the tax bill.

When Collins describes her deal, she makes it sound both ironclad — her word — and substantial. She has spoken of a personal commitment from Mitch McConnell, the Senate majority leader. And she’s emphasized that the deal isn’t merely for show. It will, she insists, protect Medicaid and Medicare — two programs particularly important to Mainers, given the state’s large elderly population.

“I also got an ironclad commitment that we’re not going to see cuts in the Medicaid/Medicare program as a result of this bill,” Collins said on “Meet the Press.”

But some of Collins’s fellow Republicans evidently have a different definition of ironclad.

Within days of the Senate vote on the tax bill, conservative House Republicans started saying that they didn’t care about her deal. She did not make it with them, and they do not feel bound by it as they negotiate the bill’s final language with the Senate. These House members, as Politico put it Friday, have decided to “thumb their nose” at Collins.