Issa's retirement moves the contest for his Southern California seat from a toss-up to one that leans in Democrats' favor, said Sabato's Crystal Ball analyst Kyle Kondik.
Issa's retirement means there's no Republican running in the 49th District, as of Wednesday morning. In fact, Indivisible has an organization committed exclusively to Royce's 39th Congressional District. Kim will drop her campaign for the county seat and open a campaign committee with the Federal Elections Commission in the coming days, said Dave Gilliard, campaign consultant to both Royce and Kim.
Royce said Kim "will be an effective voice for middle class families and for policies that keep our country secure, grow jobs and increase economic opportunities for the people of our 39th District".
Republicans, meanwhile, expressed confidence they could hold onto Issa's seat, not least because of the crowded field of Democrats.
In total, 29 House Republicans have announced they will retire at the end of this term, significantly more than is typical, according to Daily Kos Elections, and the Democratic party needs to pick up 24 seats to take back the House.
As a non-profit trade association, the chamber can raise and spend unlimited amounts of money - including on political races - without having to disclose its donors.
They are joined by other Congressmen who have already announced they will not return: Joe Barton (TX), Ileana Ros-Lehtinen (FL), Charlie Dent (PA), Dave Reichert (WA), Pat Tiberi (OH), Frank LoBiondo (NJ), Lynn Jenkins (KS), Sam Johnson (TX), John Duncan Jr. Steve Stivers, chairman of the National Republican Congressional Committee. Four are Democrats: Applegate, Mike Levin, Paul Kerr and Sara Jacobs.
And Harper's announcement followed retirement plans announced by Senate Finance Committee Chairman Orrin Hatch, R-Utah, and House Transportation and Infrastructure Chairman Bill Shuster, R-Pa. Florida Republican Gov. Rick Scott is term-limited from running for re-election and is reportedly eyeing a bid for the U.S. Senate. Together, we put an end to abusive Congressional earmarks, strengthened the Violence Against Women Act, empowered better oversight of the executive branch, and cleared the course for better intellectual property protections to stop the piracy of American ingenuity. Most humbling for me - and for anyone who represents this area - has been the special privilege of representing the Marines and Sailors of Camp Pendleton and their families.
The congressional district Issa has represented since 2001 - California's 49th - is one of 23 won by Democrat Hillary Clinton in the 2016 presidential election that are currently held by Republicans, who are now considered vulnerable in this November's congressional elections.
"Representing you has been the privilege of a lifetime", Issa said in his press release.
Several other House Republicans said in interviews Wednesday that they had been struck by the intensity of the grassroots "resistance" to Trump and Republican officeholders.