Senate Democrats are hoping to browbeat Republicans into backing their Wall Street reform proposals by casting the bill in populist terms – and Sen. Bob Casey Jr., D-Pa., is embracing the rhetoric.

“When I see the reactions by Republicans in the Senate to what we’re working on, I have to remember an old line: There they go again,” Casey said at a news conference this afternoon.

“The same crowd that protected Wall Street and the record profits for the Wall Street scheme artists, there they go again by doing one thing – saying no and stopping this legislation at all costs. The American people I think are watching very carefully about whose side you’re on.”

Casey serves on the Senate Agriculture Committee, which plans to vote on a proposal by Sen. Blanche Lincoln, D-Ark., Wednesday to regulate the derivatives market – now comprised of largely secret bets on the price of goods like agricultural products. Complex derivatives trades, including the infamous credit-default swaps, were blamed in part for the financial collapse.

Lincoln’s bill would make those transactions public and mandate that big banks spin off derivatives trading to a separate entity – so if they go south, it won’t bring the whole bank with it.

Big banks say this is an overreach that could cost them billions, but Democrats are eager for a fight with the financial industry.

“All we’re asking for is to let the sun shine in – let’s find out what’s going on,” said Sen. Tom Harkin, D-Iowa. “Why is Wall Street so afraid of a little sunshine?”

Lincoln, Harkin and Casey spoke at a news conference to tout the bill, which is expected to be merged with Sen. Chris Dodd’s reform legislation to be brought to the floor perhaps as soon as next week.