Just one year ago, the Democrats who controlled the Senate had won their latest landmark victory: passage of a bill to remake financial regulation.

Today, Democrats still run the Senate, but their agenda looks a good bit different. This week, the highlight was a vote to end tax breaks for oil companies.

As expected, they lost.

Senate Democrats are in a historically difficult spot. House Republicans have the energy. President Obama has the spotlight. And thus they have become the third wheel of democracy — with a lesser role in Washington’s broader debates, and without the votes to overcome Republican filibusters in their own chamber.

In response, Senate Democrats have adopted a minimalist agenda. They have blocked bills from the GOP-led House but proposed few broad ideas of their own — hoping to keep vulnerable incumbents from having to make controversial decisions before the 2012 elections.

This predicament has altered the way those Democrats are selling themselves. They spent the previous two years fighting for really big things — national health-care reform, changing the way Wall Street works, approving an economic stimulus package worth more than $800 billion.

Now, they are trying to do next to nothing and still have it look good.

Political circumstances make it “hard to make affirmative promises about what we’re going to do going forward,” said Sen. Sheldon Whitehouse (R.I.). “It has to be about what we’re going to not allow to happen. What we will not allow to stand.”

Where the balky Senate was once the biggest obstacle to Obama’s most far-reaching ideas, now it’s the GOP-controlled House. So the main dynamic of partisan battles has been the House vs. the White House, with the Senate on the sidelines.

House Republicans have reacted to that situation by passing a flurry of bills, trying to repeal the health-care law and expand offshore drilling. They have then blamed Democrats for letting the measures fizzle in the Senate: House Speaker John A. Boehner (R-Ohio) has made a habit of bashing “the Democrats who control Washington.”

The Senate’s votes this week on energy proposals were only the second and third to deal with legislation in the previous month. The other legislative vote was an unsuccessful effort to stop Republicans from filibustering a small-business bill that neither side showed much support for, despite it occupying five weeks of floor time.

Next week will bring another flurry of drama, with little result.

Senate Majority Leader Harry M. Reid (D-Nev.) expects to call a vote on the House Republican budget, primarily to demonstrate that Republicans are divided on the controversial proposal to turn Medicare into a privatized voucher system.

The vote will fail, as all Democrats and some Republicans are expected to oppose it.

Minority Leader Mitch McConnell (R-Ky.) plans to counter with an alternative, possibly offering Obama’s 2012 budget proposal, which both parties lambasted as being far too timid in dealing with the nation’s swelling deficit.

That, too, will fail — blocked by all Republicans and some Democrats.

This term is likely to be dominated by a few huge battles over issues on which the two sides must agree. This year, the need to pass a 2011 budget allowed Republicans to wrangle deep spending cuts. Soon, similar talks about the national debt ceiling could produce a framework that would require much deeper cuts in years to come.

Beyond that, the Democrats’ strategy is to not look for fights.

Down to 53 votes on their side of the aisle, from a high-water mark of the filibuster-proof 60 in 2009, Democrats know that their majority status is very much in jeopardy. Next year, 23 of their seats will be up for grabs, including those from conservative-leaning states such as Montana and Nebraska.

Democrats have decided to try to shield those lawmakers from the usual weeks-long debates and instead await for compromises to be reached behind closed doors. Reid’s approach is a bet that doing nothing looks better for them, so long as their arguments resonate with voters in 2012.

“Ideally, what we’d like to do is get things done to help improve our economy and create jobs. But, if we’re not able to do that because Republicans are blocking,” then it’s important to highlight the two parties’ differences, said Jon Summers, a spokesman for Reid.

Summers said he thinks Republicans are losing the energy they had at the beginning of the term: “They’re having that energy beaten out of them right now.”

Some of the Democrats may feel the same way. Sen. Christopher A. Coons, newly elected from Delaware, voted almost as many times in last fall’s short lame-duck session (51 votes) as in the first four months of this term (61 votes).

“At times I’m so frustrated, I feel like I’m banging my head against the wall trying to encourage forward movement,” Coons said last month on CBS’s “Face the Nation.”

But other senators have tried to put a good face on the situation — embracing their role as a legislative bulwark against Republican ideas. Ask Sen. Sherrod Brown (D-Ohio) what Senate Democrats want, and he will talk about what Republicans want.

“You start with what they’re doing, and what they’re doing is governing by ideology,” Brown said in an interview. He said the Senate’s role is to block GOP proposals to remake Medicare and lower taxes for the wealthy, and watch Republicans torpedo themselves.

“It’s so clear that they’re overreaching,” Brown said, arguing that Republicans will be rebuked in the 2012 elections. “I’m not concerned at all.”

The same idea shows up in home-state appearances, such as the one Whitehouse made at the Johnston Senior Center in Johnston, R.I., one recent morning. He gave a three-page statement about health care that didn’t mention the word “Democrat” once.

He did, however, mention the other guys.

“The House of Representatives recently passed a Republican budget, which proposes privatizing Medicare,” Whitehouse said. “That would be a prescription for poverty-creation.”

Other Democrats have sought to become relevant by allying themselves with Republicans. Three Democratic senators joined three Republicans in a “Gang of Six” to try to work out a bipartisan compromise on the budget. But that group began to fray on Tuesday, as Sen. Tom Coburn (R-Okla.) declared an “impasse” and walked away as the remaining five senators considered whether to forge on.

Separately, Sen. Ron Wyden (D-Ore.) has touted his work with Republicans on another headache issue: revamping the federal tax code. In a town hall meeting recently in rain-lashed Hood River, Ore., he talked up a bipartisan tax plan he had co-sponsored with Sen. Daniel Coats (R-Ind.).

“Have I mentioned he’s a Republican?” Wyden asked the crowd.

He had.

But already, this Congress has rained on Wyden’s high hopes. As the two sides reached a final deal on the 2011 budget this year, party leaders quietly slipped in a clause that erased one of Wyden’s signature accomplishments: a program that let some employees use employer-financed vouchers to buy outside health insurance.

This was bipartisanship, all right, but it underscored Wyden’s weakness in this Congress, not his influence. Wyden said neither party’s leaders would admit to having killed it.

“To have it knifed this way — and everybody says, you know, ‘I wasn’t near the mugging,’ ” Wyden said after the town hall meeting. “Pretty outrageous.”