“It’s a point of great contention with the Democrats in Congress that feel like we’re doing an awful lot to support his agenda,” Sen. Mary Landrieu (D-La.) told POLITICO on Wednesday. “And it’s very discouraging, disheartening and it’s really not fair. He may just want to keep that up, but it doesn’t help his relations with the Democratic members of Congress at all.”

As he prepares to address a joint session of Congress on Thursday in a prime-time address on the slumping economy, Democrats on Capitol Hill are urging the president to pin the blame squarely on the Republicans who control the House and the powerful GOP Senate minority for the legislative gridlock that has paralyzed Washington.

Democrats hope Obama will repeat the themes from a more partisan Labor Day speech in Detroit in which he called on the congressional GOP to “put country before party.” But it’s not that easy for Obama, who faces a delicate balancing act: He must try to create a sharp contrast with his GOP adversaries without alienating them because he’ll need their support to pass an ambitious jobs agenda that could be critical for the economy and his reelection prospects.

In the past few weeks, Obama has blasted dysfunction in Congress, without explicitly pointing a finger at Republicans.

“If they don’t get it done, then we’ll be running against a Congress that’s not doing anything for the American people, and the choice will be very stark and will be very clear,” Obama said last month at Decorah, Iowa.

The Democratic senator from Iowa, Tom Harkin, isn’t too happy about that kind of rhetoric coming from the president.

“It’s not Congress’ fault,” he said sternly on Wednesday. “It’s the Republicans who were throwing up all these roadblocks, delaying things, objecting — not Congress. If he wants to be forthright and honest to the American people, he’s got to tell it like it is.”

The frustration has been percolating in Democratic circles for months. They argue that they carried the president’s agenda across the finish line for two years and now believe there’s greater urgency to shape public perception that Republicans are the ones blocking progress.

“I personally prefer for the president to create a bright line by defining who is opposing his policies to create jobs and move the country forward versus who is supporting him,” said Sen. Robert Menendez (D-N.J.), who is up for reelection next year. “But when you just say ‘Congress,’ you draw the whole institution together, that means both Houses and both parties when in fact that isn’t necessarily the case.”

The White House’s relationship with Democrats has grown increasingly strained as of late, as Obama has tried to cut a sweeping budget deal with House Speaker John Boehner (R-Ohio) and as the president’s reelection campaign has begun to suck up cash from deep-pocketed donors who are also being courted by Senate Democratic officials.

After a speech at Johnson Controls in Holland, Mich., last month, White House spokesman Josh Earnest told reporters that the president believed Republicans were the “source of the intransigence in this debate,” calling for bipartisan agreement on job creation measures and cutting the deficit.

But in that speech, Obama placed the blame on “partisan brinksmanship” in Congress for the unprecedented credit-rating downgrade by Standard & Poor’s.

“This downgrade you’ve been reading about could have been entirely avoided if there had been a willingness to compromise in Congress,” he said.