Rising opposition from the House Democratic Caucus is imperiling a push by party leaders to deliver the lobbying overhaul they promised on the campaign trail.

With details of the reform plan sinking in a day after leaders unveiled it, Members from several corners of the Democratic Caucus said they were considering blocking the plan.

“I think it’s half of our entire Caucus,” said Rep. Dennis Cardoza (D-Calif.). “A lot of us believe the measures are unworkable. … We’re OK with tough reform, but it’s got to be written well, and this isn’t.”

Added Rep. William Lacy Clay (D-Mo.): “If the vote were held today, I don’t think they would get the numbers from Democrats.”

House leaders nevertheless are sticking to an aggressive schedule to try to rush the bill to passage before the Memorial Day break. They will try to allay concerns and answer questions about the measure in a second Caucus briefing set for this morning. Then, at 10:30 a.m., the Judiciary Committee will mark it up. If it is approved, it will hit the House floor next week.

Judiciary Chairman John Conyers (D-Mich.) acknowledged leaders have work to do to save the package from defeat. “There is sufficient misunderstanding for us to be concerned about that,” he said. But postponing consideration of the measure “would send the wrong signal,”

Leaders spent Wednesday meeting with lawmakers, in groups and one-on-one, to try to better explain the measure.

Two groups causing particular concern are the Congressional Black Caucus and the conservative Blue Dog Coalition. Both maintain generally friendly relations with business lobbyists, and senior members of each faction have raised objections to proposals that would double to two years the cooling-off period for lawmakers and staff taking lobbying jobs and require lobbyists to disclose campaign checks they bundle for candidates.

Rep. Collin Peterson (D-Minn.), a Blue Dog member and House Agriculture Chairman, said since he was unaware of any scandals relating to the revolving door question, he thinks the provision addressing it is unnecessary.

The bundling provision was not included in the overhaul package Democratic leaders introduced Tuesday, but Rep. Chris Van Hollen (D-Md.) put forward a separate plan dealing with the issue. The Judiciary panel will take it up today and it is expected to be offered as an amendment to the broader bill once it reaches the floor.

Clay, a CBC member, said the bundling language would make it tougher for Members like him who are from safe districts to fill their campaign coffers. “Because I’m considered safe, I have to cajole and plead with donors to max out,” he said. “I compare it to fishing: They make me nibble, instead of getting the full bite. And this would just make fundraising that much more difficult.” Clay said he plans to vote against both the rule governing debate on the overhaul and the package itself.

As prospects for the overhaul teeter, outside reform advocates said they are unsure whether House Democratic leaders can pull their Members together. “I’m worried about it, absolutely,” said Craig Holman of Public Citizen. He said leaders and freshmen, many of whom campaigned on cleaning up the process, will have to overcome “the old bulls of the Democratic Caucus, who don’t want to see much change.”

With an unknown number of Democrats poised to defect on the measure, its fate could ride on the level of Republican support it manages to attract. It is unclear whether GOPers would oppose the measure en bloc — as House Democrats did last year when they derided the Republican package as too weak — or follow the path of their Senate counterparts earlier this year. The Senate measure passed with overwhelming bipartisan support.

Rep. Lamar Smith (Texas), the top Republican on the Judiciary Committee, offered backhanded praise for the Democratic measure. “I am pleased Democrats chose to take up many of our original recommendations. This bill will make for more open and more responsive government.”

But House Minority Leader John Boehner (R-Ohio) laid the groundwork for possible GOP opposition, faulting the Democratic package for leaving open a loophole that exempts lobbyists for public universities and state and local governments from a new gift ban.

The bill Democrats introduced Tuesday requires lobbyists to file quarterly disclosure reports, up from the current semiannual requirement, and, for the first time, include a detailed accounting of their political contributions. Those reports would be made available online in a searchable format.

Aides would be banned from having any official contact with their boss’ spouse, if that spouse is a lobbyist. And lawmakers would have to publicly disclose negotiations for outside jobs within three days. Senior staff would have to give the ethics committee a heads-up about such talks.

To address the “K Street Project” — the Republican campaign to install their own in top lobbying jobs — the measure would subject anyone on the Hill trying to strong-arm private-sector hiring decisions to up to 15 years in prison.

Once Members and senior staff have left the Hill, they would have to wait two years, double the current period, before directly lobbying their former colleagues.

But the bill also leaves out many provisions reformers call key. Lobbying firms that get hired to gin up constituent contacts with Congress would not have to register or report their activities. Pending the fate of the Van Hollen amendment, lobbyists would not have to disclose checks they gather and then deliver to candidates.

On the revolving door, while former lawmakers and staff would have to cool their heels for two years before heading back to lobby on the Hill, they could still conduct backroom strategy sessions during that period. Reformers have been shopping for a lawmaker to propose expanding the scope of that provision.

The measure does not call for a new independent office to replace the ethics committee and help enforce the laws, a top priority for reformers. Instead, a bipartisan task force is examining the issue and will deliver its findings this month. Democratic freshmen have rallied behind a proposal to outsource ethics policing duties and will try to offer it as an amendment to the reform bill.