Nearly two years after the signing of a major law to boost oversight of Wall Street, two Democratic senators are calling on President Obama to speak out even more strongly in favor of a new federal rule that they say should have banned the trading that led to JPMorgan Chase’s $2 billion or more loss.

But Obama is in a difficult spot. Although he introduced and supports the Volcker Rule, which bans banks from gambling with their own money, regulators have yet to finish writing the rule and haven’t determined whether the trading would have violated the draft version of the rule that has been released.

In his remarks since the JPMorgan debacle, Obama has stressed that the trading losses underscore how new regulations are making the financial system stronger and show the need for putting more rules into place.

Last week, the authors of the Volcker Rule called on Obama to speak out in favor of a tougher version of it.

“There is no way they should be silent in this matter,” said Sen. Carl Levin (D-Mich.), one of the authors of the Volcker Rule. “It’s my hope they’ll speak out very clearly on this subject.”

JPMorgan has cast doubt on whether the Volcker Rule would have precluded the trading. Financial regulators and a senior Obama administration official say it’s too soon to tell.

The issue turns on whether the bank was using the large trade to hedge risks in other investments or using the trades to speculate for profit. If JPMorgan was trying to hedge risks, the official said, the Volcker Rule might not have prevented the trades. However, if the bank was speculating under the guise of hedging, the activity would have likely been banned.

In his weekend radio address, Obama did not directly cite the Volcker Rule. Rather, he said the financial reform “discourages big banks and financial institutions from making risky bets with taxpayer-insured money” and “we can’t afford to go back to an era of weak regulation and little oversight.”

Obama has pointed out that JPMorgan survived the losses, because the firm and other banks have been forced to hold a lot more money in reserve as a buffer against potential losses.

“While that bank can handle a loss of that size, other banks may not have been able to. And without Wall Street reform, we could have found ourselves with the taxpayers once again on the hook for Wall Street’s mistakes,” he said.

The Volcker Rule is being written by five federal agencies, which are independent of the Obama administration. Treasury Secretary Timothy F. Geithner is playing a coordinating role.

Republicans also are facing new pressure because of the JPMorgan losses. Last week, House Republicans had to postpone plans to try to roll back new rules governing derivatives — the type of financial instrument at the center of the JPMorgan debacle.

“As always, Washington has a tendency to overreact,” said House Agriculture Committee Chairman Frank D. Lucas (R-Okla.). “However, this committee will take the time to gather all relevant information before we proceed to ensure there are no unintended consequences of the legislation that would encourage recklessness in our financial institutions.”

Republicans have introduced a variety of other proposals to roll back elements of Dodd-Frank, including a proposal that would limit the government’s ability to safely wind down a large bank if it should be at risk of failure.

The regulatory fallout underscores how the legacy of one of Obama’s signature domestic achievements falls largely, though not completely, outside his control.

“Given that the Volcker Rule has been violated by JPMorgan in this wild bet and given that Treasury is point on it, there certainly is some political risk to the president if they actually don’t come out with a rule, come out with one quickly, [or] come out with one that doesn’t favor Wall Street,” said Dennis Kelleher, president of an advocacy group called Better Markets.

He added, if the rule “allows Wall Street do what JPMorgan did, it’s a complete failure and there should be a political price.”

On the Democratic side, Levin said last week that Gene Sperling, head of the National Economic Council, called him earlier in the week to talk about the issue. Levin said he understood that the White House and the Treasury have only limited ability to shape the new rules, given that they are being written by officials at banking regulatory agencies that by law are independent.

“They have a right to express an opinion. They may not make the decision . . . but they have a right to have an opinion,” he said.

Michael Greenberger, a University of Maryland professor and former federal regulator who helped write parts of the Dodd-Frank bill, said the White House’s perspective has had difficulty gaining traction.

“The weight of the commentary has been overwhelmed by the banks and their lobbying institutions,” he said. “I think the White House in some sense had been drowned out. I think this [JPMorgan episode] has given it a platform have its message heard more clearly.”