1966 United States House of Representatives election in Delaware

Throughout the campaign, Roth appeared alongside his wife, Jane, and their dog, Ludwig. Roth stated that he hoped to shake hands with 50 thousand voters. He frequently wore a yellow button reading "I am Bill Roth",^[8] Roth had previously worn the button during his unsuccessful 1960 campaign for Lieutenant Governor of Delaware.^[15]

During the campaign, Roth aggressively criticized then-President Lyndon B. Johnson, particularly his foreign policy. Cy Liberman of The Morning News joked that Roth was "running against the President of the United States in addition to the Democratic Congressman."^[8] McDowell made a similar comment saying that Roth was "running against President Johnson, the Department of Defense and all the liberal legislation passed in the past six years." He further criticized Roth, saying that his political positions were unclear.^[16] On October 28, 1966, Roth and McDowell participated in a debate at the University of Delaware. The debate was sponsored by the Student Government Association. Questions were written by students of the university's political science department.^[17]

During the campaign, John J. Smith, a Republican candidate for the state legislature, claimed there were irregularities with voting registration. Smith asked the United States Department of Justice to investigate and monitor the election, but was rejected due to a lack of legal basis for the request.^[18] A report by the grand jury of New Castle County found that there was some evidence of illegal activity, including voters participating in primaries for parties they were not registered for and allowing them to vote without proper voter identification.^[19] A list of absentee voters was made available to select Democratic candidates, including McDowell. No Republicans received the list, Delaware GOP chairman Clayton S. Harrison criticized this decision, referencing the findings of the grand jury report. Reportedly, McDowell used the list to send out campaign materials.^[20]

The election took place on November 8, 1966, concurrently with various other elections.^[21] Like with most cycles the President's party struggled, losing 47 house seats along with various governorships and Senate seats.^[5][6] Roth defeated McDowell by around 11 percent of the vote. He received 97,268 votes, nearly 30 thousand more than McDowell's 67,281. Roth received the second highest number of votes of any Republican candidate elected at-large, behind only incumbent Insurance Commissioner Robert A. Short.^[21]

Additionally, Roth won all three of Delaware's counties. His strongest showing was in New Castle County where he received 66,871 votes. McDowell's strongest showing was also in New Castle County where he received 49,718 votes. The closest was Kent County where Roth won by just 723 votes.^[22]

General election results^[21]

Party		Candidate	Votes	%	±%
	Republican	William Roth	90,561	55.77%	12.4
	Democratic	Harris McDowell (Incumbent)	72,142	44.23%	12.3
Total votes			162,703	100.00%
	Republican gain from Democratic

Following his victory, Roth resigned from his position as a senior councilman at Hercules Inc.^[7] McDowell, like several other lame duck representatives, McDowell was set travel to Europe as part of a congressional delegation.^[23] However, he, alongside fellow Democratic representatives Ronald B. Cameron of California and Roy H. McVicker of Colorado, decided to cancel his trip. When asked why, McDowell explained that he did not believe it was fair for an outgoing congressman to go abroad.^[24]

McDowell and Roth competed again in the following election; Roth won re-election, increasing his margin of victory to seventeen points.^[25] Following the second loss, McDowell retired from politics.^[26] During Roth's second term, he resigned from the House to fill a vacant Senate seat.^[27] He was succeeded by Republican state representative Pete du Pont.^[28] McDowell was the last Democrat to represent Delaware in the House until Delaware Treasurer Tom Carper's 1982 victory.^[22][29] After his defeat, McDowell was appointed to a position within the Government of Delaware by then-Governor Charles L. Terry Jr.^[7] Despite this, during the following election Terry endorsed candidates to run against McDowell in the Democratic primary.^[30]