From big banks' exotic trades to the credit cards in people's wallets, it only takes a few of the most contentious issues to upend a careful political equilibrium as lawmakers try to blend House and Senate bills into a single rewrite of US banking regulations. The final measure, which President Barack Obama wants by July 4, is intended to prevent another financial crisis like the 2008 meltdown, which triggered a deep recession. Rep. Barney Frank, chairman of a panel resolving differences in the two bills, and Sen. Christopher Dodd, who shepherded the Senate's measure, must fend off industry efforts to dilute the final legislation. And they will need to hold together a fragile Senate coalition that included only four Republicans. Typically, legislation gets watered down in the Senate. This time, the Senate version emerged tougher than the House bill. Frank agreed to make the Senate bill the base, with some minor House modifications. There's momentum behind the Senate version. “Throughout this process you have seen a desire by members not wanting to be seen voting with the banks,” said Edward Mills, a financial policy analyst at FBR Capital Markets.The financial industry is no stranger to the lawmakers working on the legislation. At least 56 industry lobbyists have served on the personal staffs of the 43 Senate and House members who will have a hand in shaping the bill over the next two weeks, according to an analysis by Public Citizen and the Center for Responsive Politics, two government watchdogs. What's more, the center found that lawmakers on the committee settling differences between the competing House and Senate versions have received more than $112 million over two decades from political action committees or employees of industries affected by the legislation. “It's going to be very difficult to stop special interests, working through some members of the conference, from inserting weakening provisions,” said Travis Plunkett, legislative director of the Consumer Federation of America. The main issues to be settled Derivatives: These are the complex, unregulated securities that many corporations typically use as a hedge against market fluctuations. For instance, an airline may try to soften the cost of a potential rise in fuel prices by betting in the derivatives market that fuel prices will rise. But derivatives have become instruments for risky speculation. The legislation would require that they be traded in regulated exchanges. The toughest Senate provision would force banks to shed most of their lucrative derivatives business - the trades they conduct for themselves and the markets they create for clients would have to be spun off into separate subsidiaries. The proposal's chief advocate is Sen. Blanche Lincoln of Arkansas, who survived liberal and labor attacks during a hard-fought Democratic primary runoff largely by spotlighting her anti-Wall Street stance. The Obama administration and bank regulators, including Federal Reserve Chairman Ben Bernanke, have said her proposal goes too far. Advocates say it would limit the type of risky bank behavior that led to the financial crisis. Large banks are simply apoplectic, watching as it gains strength over time. Lincoln's political success had two effects: It boosted her strength as a member of the House-Senate conference committee working on a compromise and it showed other Democrats that her Wall Street criticism worked in a tough political year for incumbents. With seven Senate Democrats and five Senate Republicans on the conference committee, Frank and Dodd can't afford to lose her vote. Volcker Rule: After the Great Depression of the 1930s, depository banks and investment banks had to be separate and independent enterprises. Congress and the Clinton administration changed that in 1999. Now, huge financial institutions such as Goldman Sachs, Morgan Stanley, JPMorgan Chase and Bank of America combine commercial and investment banking operations. A Senate plan known as the Volcker rule, after former Fed Chairman Paul Volcker, would prohibit banks from betting on the markets with their own money. It would give regulators the authority to determine the best way to put into place that prohibition, which would apply to all securities trades, not just derivatives. Unlike Lincoln's plan, it would not stop banks from creating trading markets for their clients. Volcker is the proposal's leading champion. But he and several Democratic lawmakers want to strengthen the Senate bill by giving regulators less latitude to modify the prohibition. The idea has been pushed by Democratic Sens. Carl Levin of Michigan and Jeff Merkley of Oregon. Prompted by a Securities and Exchange commission case against Goldman Sachs, their plan also would prevent financial firms from betting against securities they assemble for their clients. Large banks see billions of dollars in trades slipping away. They prefer a House plan that merely says regulators could ban such trades. But Frank last week dashed those hopes. “The general direction that Sens. Merkley and Levin were moving in is a direction that a lot of people are supportive of,” he said. “The final version, we'll see. But it will be tougher than the House.” Debit card fees: People in the US use debit cards more frequently than credit cards. But their use costs merchants money: For every swipe, merchants pay 1 percent to 2 percent to banks and credit card networks such as Visa and MasterCard. A proposal that passed the Senate 64-33 requires the Federal Reserve to limit those fees, and it has created a lobbying donnybrook between banks and retailers. Most of the fees go to banking giants such as Bank of America and JPMorgan Chase. But the face of the lobbying effort has been small community banks and credit unions that say they will be disproportionately hurt if they lose such fees. The proposal specifically excludes banks with assets under $10 billion. Officials at small banks say their banks still would have to lower fees to compete with bigger banks or drop their debit card programs. Though the House did not take up the measure, the Senate vote sent a strong signal. “When you have 64 senators voting for something like that after a lot of controversy it's unrealistic to think it's going to go away,” Frank said. Analysts say the measure could be amended, perhaps by expanding the conditions that the Fed would have to consider in setting the fees.