Hoyer Challenges Issa to Show E-Mails WASHINGTON - With the House just days away from a vote on holding Attorney General Eric H. Holder Jr. in contempt, Representative Darrell Issa, Republican of California, appeared on national television on Sunday to say he had e-mails showing that the architects of a federal gun-smuggling investigation intended to use the operation to build a case for reinstating the lapsed ban on assault-weapons sales. "We have e-mail from people involved in this that are talking about using what they're finding here to support the - basically assault weapons ban or greater reporting," Mr. Issa, the chairman of the House Oversight and Government Reform Committee, said on ABC's "This Week." On Tuesday, Representative Steny H. Hoyer, Democrat of Maryland and the House minority whip, challenged Mr. Issa to prove it. "If he has those documents, he should show them," Mr. Hoyer said. The issue is one of the underlying factors that have turned the gun program, Operation Fast and Furious, into a cause célèbre among conservatives. The investigation, run by the Phoenix office of the Bureau of Alcohol, Tobacco, Firearms and Explosives from late 2009 to early 2011, allowed guns purchased in the United States to "walk" across the border into Mexico, where some found their way into the hands of violent drug traffickers. Conservatives have speculated that the operation's tactics were devised to build a case for greater gun control in the United States. Republicans on the Senate Judiciary Committee, which has conducted the investigation into Fast and Furious with Mr. Issa, said they have found no e-mails mentioning the assault weapons ban. Among the thousands of pages of internal e-mails and documents Congressional investigators have gathered about the operation, they found a few - from well after the operation began showing that A.T.F. officials considered using some examples of gun flows documented in the case to build a case for requiring greater reporting of multiple "long gun" (rifle) sales by federally licensed gun shops. They singled out AK-47 assault-style rifles and their variants. An e-mail dated Jan. 4, 2011, by William Newell, the Phoenix A.T.F."s special agent in charge of Fast and Furious, talked about news media strategy, mentioning "the associated firearms trafficking of 49 AKs that were purchased in very short order by a diverse group of straws (another reason to mention the long-gun reporting issue)." An attached A.T.F. memo on firearms tracing and drug-trafficking organizations, or D.T.O."s, says, "These cases demonstrate the ongoing trafficking of firearms by Mexican D.T.O."s and other associated groups operating in Arizona and the need for the reporting of multiple sales for certain types of rifles in order to ferret out those intent on providing firearms to these criminal groups." Such documents were first reported by CBS News in December 2011. The A.T.F. proposed requiring gun dealers along the Southwest border to report bulk sales of long guns - as dealers across the country were already required to do for bulk sales of handguns - in December 2010, invoking a hurry-up procedure for emergencies. But the proposal ran into trouble with the Obama administration's Office of Management and Budget, which rejected the request by saying it did not qualify as an emergency. In November 2011, the regulation was approved under the regular process. But the documents supplied by the Senate Judiciary Committee refer to the A.T.F."s existing right to issue "demand letters" to gun dealers, not to any new push for gun control legislation. And the term "assault weapons ban" does not appear. The assault weapons ban, which was instituted in the first term of the Clinton administration but was allowed to lapse during the Bush administration, marked the nadir of gun rights, according to gun advocates and their supporters on Capitol Hill. Representative Elijah E. Cummings of Maryland, the ranking Democrat on the House Oversight Committee, said Tuesday that he did not believe the e-mails exist building a case for reinstating the ban. "And I think it is unfortunate people are coming up with these theories," he said. The Caucus asked aides of Mr. Issa on Monday morning to show the e-mail on the assault weapons ban that the chairman had referred to. None have been shown.