Committee assignments

• Committee on Education and Labor
  • Subcommittee on Early Childhood, Elementary and Secondary Education (Ranking Member)
  • Subcommittee on Higher Education, Lifelong Learning, and Competitiveness
• Committee on Financial Services
  • Subcommittee on Capital Markets, Insurance, and Government-Sponsored Enterprises
  • Subcommittee on Financial Institutions and Consumer Credit
  • Subcommittee on Domestic Monetary Policy and Technology

In 1992, Castle could not run again for Governor, due to constitutional term limits. The result was what became known as "the Swap." Castle ran for the seat of U.S. Representative Tom Carper and Carper ran for Governor. Delaware's political leadership had quietly worked out the arrangement and retained the services of two very popular office holders.

Castle was first elected U.S. Representative in 1992, defeating former Lieutenant Governor Shien Biau Woo. Since then, he won election by wide margins eight times, defeating Democrats Carol Ann DeSantis in 1994, Dennis E. Williams in 1996 and 1998, Michael C. Miller in 2000 and 2002, Paul Donnelly in 2004, Dennis Spivack in 2006, and Karen Hartley-Nagle in 2008.

Castle was the co-chair of several Congressional caucuses, including the Diabetes Caucus, the Community College Caucus, the Biomedical Research Caucus and the Passenger Rail Caucus. He was also considered one of the most moderate Republicans in the U.S. House. In the wake of Tom DeLay's indictment in September 2005, liberal columnist E.J. Dionne named Castle as one of four lawmakers capable of leading an anticorruption reform of the Republican Party. Castle was a member of various liberal Republican Organizations, such as Republicans For Environmental Protection, The Republican Majority For Choice, Republicans For Choice, and Christine Todd Whitman's Its My Party Too. He is pro-choice and supports some gun control measures.^[9] He voted against a constitutional amendment that would have banned same-sex marriage.^[10] The non-partisan National Journal gave Mike Castle an ideological composite score of 59% conservative and 41% liberal.^[11]

Castle's centrist positions served him well in a state that trended increasingly Democratic during his tenure in the House. Delaware had long been reckoned as a bellwether, but has voted Democratic in every presidential election since 1992, due almost entirely to heavily Democratic New Castle County. At the same time, his centrist record made him the target of conservative groups such as Club for Growth, who ranked him the least conservative Republican in the U.S. House in 2008, and RemoveRINOs, who, in April 2010, named him the Ace of Spades on its most-wanted list.

In February 2004, Castle sponsored H.R. 3831 to reauthorize the assault weapons ban of 1994. The bill was co-sponsored by 11 Republican colleagues and 129 Democrats.^[12] In June 2008, Rep. Mark Kirk, R-IL, introduced H.R. 6257 to reinstate the ban, and Castle was one of the bill's four Republican co-sponsors.^[13] Both bills died in committee.

Castle cosponsored the Stem Cell Research Enhancement Act. The bill proposed expanding the number of embryonic stem cell lines that are eligible for federally funded research, expecting that this funding would generate more research and ultimately greater progress in developing new treatments for a wide range of medical conditions. Presently, the only embryonic stem cell lines eligible for federal funded research were derived before August 9, 2001. This legislation removes that date restriction, along with proposing stronger ethical requirements. After successfully passing both the U.S. Senate and the U.S. House, it received U.S. President George W. Bush's first presidential veto in July 2006.

In December 2010, Castle was one of fifteen Republican House members to vote in favor of repealing the United States military's "Don't Ask, Don't Tell" ban on openly gay service members.^[14][15]

During his term in Congress, Castle was known for his interest in numismatics. In 1995, he authored the legislation that created the American Platinum Eagle platinum bullion coin. He later sponsored the legislation that created the 50 State quarters, Sacagawea dollar, presidential dollar coins, and America the Beautiful quarters programs, and several commemorative coins.^[16] His activity led the Numismatic Guaranty Company to deem him "The Coinage Congressman."^[16] Castle drafted one sentence of the 1997 Omnibus Consolidated Appropriations Act: "Notwithstanding any other provision of law, the Secretary of the Treasury may mint and issue platinum coins in such quantity and of such variety as the Secretary determines to be appropriate." His intent was to make it easier for the Treasury to mint platinum coins for the coin collector market, but the sentence allows the Treasury Department to mint platinum coinage in any denomination. In the event that Congress refused to raise the U.S. debt ceiling, the Treasury could thus mint a trillion-dollar coin to avoid default. This maneuver has been proposed by some commentators, but has never been done.^[17]

Castle suffered two minor strokes during the 2006 campaign, but fully recovered. Considering the general Democratic sweep of other offices, he won the election comfortably, but with a greatly reduced margin over previous years. Despite the increased Democratic sweep of the 2008 election, he, unlike many Republicans, managed to increase his margin of victory, winning over Democratic challenger Karen Hartley-Nagle by 23 points. Considering his moderate profile, popularity, and long history of service to the state, his victory was not considered surprising. Castle appeared in the documentary, Keeping the Peace, which focused on Michael Berg's 'anti-war' campaign for Castle's congressional seat in 2006. It premiered at the Philadelphia Independent Film Festival in 2009 and won the Audience Award.

On November 9, 2009, Congressman Castle's District was profiled by Stephen Colbert in his segment "Better Know a District."

Town hall

A town hall style meeting organized by Castle to discuss health care reform with constituents^[21] was featured on the Drudge Report with the headline "VIDEO: Congressman's town hall erupts over Obama birth certificate ...".^[22] The story was linked to a tape^[23] documenting a few minutes of the event and hosted on YouTube. The incident sparked discussion of the topic in relation to the moderate Republican congressman and commentators' surprise at the audience reaction.^[24][25][26] Castle was heckled and booed after calmly responding to a protester, "If you're referring to the President there, he is a citizen of the United States."^[21]

Reporting in the international press on the explosion of interest in the subject focused on the central role of the Castle incident. The British newspaper The Guardian reported:

But the real impact has been a video that has garnered hundreds of thousands of hits on the web (in which Congressman) Mike Castle, address(es) a town hall meeting on health care in Delaware last month when a woman suddenly stands up waving a bunch of papers ... The encounter was a warning to Republican officials how far the conspiracy theory has permeated parts of their party.^[27]