California's 4th congressional district

As of 2006, Republicans had 48 percent of voter registrations, Democrats had 30 percent, and Libertarians had roughly 5 percent.[5]

A Democratic congressional candidate nearly won the district in 2008, losing by only half a percentage point and less than 1,600 votes, indicating that the district was much more competitive than it appeared to be. But in the more recent 2018 and 2020 elections the Republican candidate won over 53% of the vote.[6]

New district boundaries for the 2012 elections shifted the population center to the south and east. Registered Democrats and Independents/Decline to State voters in the new district area outnumber registered Republicans by 12%. However Republicans, Independents/Decline to State and small third parties outnumber Democrats well over a 2 to 1 ratio. There are 183,800 Republicans, 117,300 Democrats and 97,200 other..

While 2018 saw 7 of California's Republican held House seats fall to Democrats, Republican Tom McClintock held his district by more than 8% over Democrat Jessica Morse.[7]

In presidential elections, Donald Trump won the district in 2016 with 54% of the vote and won in 2020 with 53.7% of the vote.

Election results from statewide races
Year	Office	Results
1992	President	Bush (R) 40.7 - 33.9%
	Senator	Herschensohn (R) 50.0 - 39.7%
	Senator	Feinstein (D) 46.0 - 45.2%
1994	Governor	Wilson (R) 66.4 - 29.0%
	Senator
1996	President	Dole (R) 51.3 - 37.8%
1998	Governor
	Senator
2000	President[8]	Bush (R) 58.1 - 36.9%
	Senator[9]	Campbell (R) 51.1 - 41.8%
2002	Governor[10]	Simon (R) 58.5 - 30.6%
2003	Recall[11][12]	Y Yes 70.4 - 29.6%
		Schwarzenegger (R) 60.6 - 17.6%
2004	President[13]	Bush (R) 61.3 - 37.4%
	Senator[14]	Jones (R) 55.6 - 40.1%
2006	Governor[15]	Schwarzenegger (R) 72.2 - 22.8%
	Senator[16]	Mountjoy (R) 50.2 - 44.3%
2008	President[17]	McCain (R) 54.0 - 43.8%
2010	Governor[18]	Whitman (R) 55.3 - 39.3%
	Senator[19]	Fiorina (R) 59.5 - 33.7%
2012	President	Romney (R) 57.9 - 39.5%
	Senator	Emken (R) 58.5 - 41.5%
2014	Governor	Kashkari (R) 55.1 - 44.9%
2016	President	Trump (R) 54.0 - 39.3%
	Senator	Harris (D) 63.3 - 36.7%
2018	Governor	Cox (R) 59.5 - 40.5%
	Senator	de Leon (D) 54.7 - 45.3%
2020	President	Trump (R) 53.7 - 43.9%

In 2018, six Democratic candidates filed statements of candidacy with the Federal Election Commission (FEC).[69] They were, in alphabetical order by last name: Regina Bateson; Roza Calderon; Richard Martin; Robert Lawton; Jessica Morse; and Rochelle Wilcox. Martin and Wilcox[70] dropped out of the race, with Wilcox[71] endorsing Morse in February.

Retired Air Force Lieutenant Colonel Charlie Brown, who was the Democratic nominee for this seat in 2006 and 2008, was "seriously considering" running in 2018,[72] but decided in June 2017 against a third campaign. In January 2018, Brown endorsed Morse for the nomination.[73] Bob Derlet,[74] the Democratic nominee in 2016, also endorsed Morse in January.

On the Republican side, McClintock has one challenger, Mitchell Kendrick White, who filed with the FEC in January.[75]

In February, the California Democratic Party (CDP) endorsed[76] Jessica Morse in a contested Democratic Nomination. Roza Calderon was able to successfully collect 322 CDP-credentialed delegate signatures needed to block the endorsement, in which Morse only received 44 delegate votes. However, CDP staff refused to accept the forms after it was alleged they closed doors early to prevent the submission. A petition was later filed with the Compliance Review Commission (CRC)[77] by Calderon. The CRC voted to accept and count the signatures, ultimately disqualifying enough signatures to proceed with Morse's endorsement. California allows candidates to include their professional description under their names on the ballot. Regina Bateson later challenged Morse's ballot designation title of "National Security Fellow" at the Sacramento Superior Court after months of controversy that Morse, who had not worked in three years, was "fluffing" her credentials.[78] California's Secretary of State, Alex Padilla, had struck down Morse's 3 ballot designations before Judge Gevercer ruled[79] that she presented "no credible evidence" to use the ballot designation of "National Security Fellow". Instead, he held that this title would mislead the average person about her recent activities. In the official Certified Candidate List,[80] Morse's ballot designation was left blank.

Under the California jungle primary (aka nonpartisan blanket primary) system, only the two candidates with the most votes on June 5, regardless of party, went on to the general election on November 6. Both Republicans and four Democrats appeared on the jungle primary ballot.[76] Morse finished second in the nonpartisan blanket primary in June 2018.

Morse was denied "National Security" as her ballot designation[81] for the November ballot. In the November general election, McClintock held the district with an advantage of more than eight points.[82]

• List of United States congressional districts

• GovTrack.us: California's 4th congressional district
• California Citizens Redistricting Commission: wedrawthelines.ca.gov 2012 final district maps