Sen. Harry Reid (D-Nev.). (Brendan Hoffman/GETTY IMAGES)

Opening the Senate on Monday afternoon, Reid did not mention either former House speaker Newt Gingrich (Ga.) or Sen. Scott Brown (Mass.) by name. But he alluded to recent comments by both Republicans on Medicare in arguing that “sometimes it’s difficult to tell where the Republican Party stands on the issue.”

“We all saw how quickly one prominent Republican presidential candidate spun himself into circles last week,” Reid said in a veiled reference to Gingrich. “First he called the plan for what it is: radical. He said it was ‘right-wing social engineering.’ Hours later, after Republicans jumped all over him, he reversed course and said he supports the plan to kill Medicare.

“Another prominent Republican, one who serves in this body, has been all over the map as well,” Reid continued, in a reference to Brown. “First he said — in his words — ‘Thank God’ for the Republican plan to kill Medicare. Then he said he was undecided. Now he says he opposes it. We’ll tune in tomorrow to see if he changes his mind again.”

Reid also criticized the Republican budget’s proposed Medicare changes more broadly, claiming that “there’s a lot in there to fear” and that it “would shatter a cornerstone of our society and would break our promise to the elderly and the sick.”

Reid’s remarks were the latest indication that Democrats are doubling down on their criticism of the House Republican budget plan, which would overhaul Medicare for future seniors. His comments came one day before a special House election in Upstate New York in which Democrats have used the Medicare argument as a cudgel against the GOP candidate, and three days before the Senate is slated to vote on the Ryan plan.

Gingrich last week apologized to Ryan after saying on NBC’s “Meet the Press” a few days earlier that the House Republican budget plan would go too far in its Medicare changes, which Gingrich said amounted to “right-wing social engineering.” Ryan and other House Republicans responded by sharply criticizing Gingrich for the comments.

The Medicare issue has also proved a tricky one for Brown, who this month told a Massachusetts newspaper that he planned to vote for the House Republican budget when it came up on the floor of the Senate. Brown’s office later clarified that the he meant that he would vote on the budget, not necessarily for it.

But on Monday, Brown signaled in a Politico op-ed that he will vote against the budget when it is up for a vote on Thursday.

“I plan on continuing to work with people of goodwill — in either party — to solve the very real problems we face,” Brown wrote. “Our country is on an unsustainable fiscal path. But I do not think it requires us to change Medicare as we know it. We can work inside of Medicare to make it more solvent.”