So the Senate just voted to end debate on Gina McCarthy as head of the Environmental Protection Agency — one of the nominations Democrats had insisted on as a condition for not changing the Senate rules by the nuclear option.

Yes, Mitch McConnell had previously admitted McCarthy had the votes to break the GOP filibuster. But McCarthy passed cloture by a surprisingly large margin — 69-31 — with over a dozen Republican Senators voting for her. (She cleared the final vote with 59 Senators supporting her.) This, after far right Senators such as David Vitter had essentially threatened to burn down the Senate to block McCarthy’s nomination.

In other words, the deal Dems forced earlier this week is holding, and then some. There are tentative signs that more Senate Republicans are willing to cooperate and work with Dems, and are losing their appetite for the GOP leadership/hard right alliance’s pact to do everything in their power to render government during the Obama era as dysfunctional as possible.

Democrats are looking at recent developments and pushing the line that Mitch McConnell is losing control of the GOP caucus. I’d say that conclusion is premature at best — GOP obstructionism, and gridlock and dysfunction, is likely to remain alive and well.

But there is one test case coming up that Dem aides are keeping an eye on for further clues to what’s going on among Republicans: The transportation and housing bill.

Next week, Harry Reid is expected to begin debate on the transportatio and housing package, which has already provoked a schism among Senate Republicans. Six Republican Senators voted for the bill at the committee level, angering conservative groups who say it doesn’t cut spending enough. Susan Collins, one of the Senators who voted for it (and who has repeatedly broken with the leadership), angrily denounced conservative attacks on the bill, insisting the lower levels of funding conservatives were insisting on was irresponsible when it came to preserving transportation and housing programs.

Democratic aides say they will watch Republican conduct next week to see whether there is a genuine split emerging in the GOP caucus. As one aide noted to me, the question is whether McConnell will be able to reassert control over the Republicans who voted for the bill in committee — and other Republican Senators who might be inclined to support the bill, partly out of parochial reasons and partly because infrastructure spending has historically gotten bipartisan support — and get them to oppose it when it comes to the floor.

Democrats view the transportation bill as another step in testing whether Republican Senators can be peeled off to support some kind of budget deal that would end the sequester. “It would be a good sign if we can move this bill on a bipartisan basis with the support of rank and file Republicans, even if McConnell doesn’t like it,” one Dem aide says.

In the wake of today’s McCarthy vote — and the decision by Republican Senators to break with McConnell — Dems are a bit more optimistic about a thaw than they were only last week. Next week’s activities should help determine whether they are right.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.