Longtime Senate Democratic Leader Harry ReidHarry Mason ReidDems walk tightrope on Pompeo nomination The Memo: Teens rankle the right with gun activism Dems to party: Go on offense with Trump’s alleged affairs MORE (D-Nev.) announced Friday that he will not seek reelection next year, triggering a race among his lieutenants to replace him.

Reid's departure also opens up top swing seat and deprives Republicans of their hopes to take out the Democratic leader.

In a video announcing his decision, Reid played down speculation that injuries to his ribs and face — which have left the 75-year-old wearing bandages and corrective eyewear — were a factor in his decision. 

"I have had time to ponder and to think," he said in the video, referring to time off after his injuries. "We’ve got to be more concerned about the country, the Senate, the state of Nevada than us, and as a result of that, I’m not going to run for reelection."

He also said he had no worries about being reelected if he ran for a sixth term.

"The decision that I’ve made has absolutely nothing to do with my injury, it has nothing to do with my being minority leader, and it certainly has nothing to do with my ability to be reelected, because the path to reelection is much easier than it probably has been any time that I’ve run for reelection,” he said.

Reid has been the Democratic leader since 2005, after his predecessor Sen. Tom Daschle (D-S.D.) was defeated in 2004.

Reid became Senate majority leader in 2007 after the wave election that left Democrats in control of the House and Senate. He helped move ObamaCare through the Senate, when Democrats enjoyed a huge majority after the 2008 elections. 

Republicans regained control of the Senate in the 2014 elections, which led to Reid and his longtime rival Sen. Mitch McConnellAddison (Mitch) Mitchell McConnell32 male senators back Senate women's calls to change harassment rules Duckworth brings her baby to Senate vote, drawing a crowd FreedomWorks backs Jim Jordan for House Speaker MORE (R-Ky.) shifting positions.

Senate Minority Whip Dick DurbinRichard (Dick) Joseph DurbinHannity, Kimmel, Farrow among Time's '100 Most Influential' The Hill's Morning Report: 200 Days to the Election Dems walk tightrope on Pompeo nomination MORE (D-Ill.) and Sen. Charles SchumerCharles (Chuck) Ellis SchumerHouse Republicans push Mulvaney, Trump to rescind Gateway funds Congress should build on the momentum from spending bill Corker won’t campaign against Democrat running for Tennessee Senate seat MORE (D-N.Y.) are the No. 2 and 3 Senate Democrats, and are expected to battle to replace Reid. Sen. Patty MurrayPatricia (Patty) Lynn MurrayDuckworth brings her baby to Senate vote, drawing a crowd Maternal deaths keep rising in US, raising scrutiny Senators press administration on mental health parity MORE (Wash.), who serves as the Senate Democratic Conference secretary, could also seek the post.

In Schumer's statement on Reid's departure, there was no mention of the coming battle over the conference's top spot.

"Harry is one of the best human beings I’ve ever met," Schumer said in a statement. "He has left a major mark on this body, this country, and on so many who have met him, gotten to know him, and love him."

Murray was equally effusive with her praise.

"He understands what members need for their constituents, how far they can be pushed when needed, when to hold us all together, and when to encourage us to go our own ways," she said in a statement.

"Like the boxer he once was, Harry knows when to throw a punch, when to keep the gloves up, and although this didn't happen very often, when to throw in the towel and live to fight to another day."

Reid would have been a top target for Republicans in 2016. He won a tough reelection battle in 2010 over Republican Sharron Angle, who was not seen as a top-tier candidate.

Reid indicated his decision to not seek reelection was motivated by some political calculations. He said he didn't want to use resources that could help Democrats elsewhere in 2016, as they try to win back the Senate in a year when Republicans are largely on defense. 

"We have to make sure that the Democrats take control of the Senate again. And I feel it is inappropriate for me to soak up all those resources on me, when I could be devoting those resources to the caucus, and that’s what I intend to do," he said in the video. 

The New York Times was the first to report on Reid's decision to retire from the Senate.

Reid's vaunted political machine will likely rally around a candidate to replace him in Nevada. Potential replacements include former Nevada Attorney General Catherine Cortez Masto, who is close with Reid, and former Nevada Secretary of State Ross Miller. Former Nevada Lt. Gov. candidate Lucy Flores could also be in the mix.

On the GOP side, strategists continue to hope they can woo Nevada Gov. Brian Sandoval into the race, though he's shown no interest in being senator and most think he won't run.

Nevada Lt. Gov. Mark Hutchison and Nevada state Senate Leader Michael Roberson, both of whom are close to Sandoval, are viewed as potential establishment Republican candidates, while former Nevada Lt. Gov. Brian Krolicki is also looking at the race. Las Vegas City Councilman Bob Beers, who's aligned with the Tea Party, is already running.

Democratic Senatorial Campaign Committee Chairman Jon TesterJonathan (Jon) TesterThe Hill's Morning Report: 200 Days to the Election Koch network targets Tester with new six-figure ad buy Senators grill alleged robocall kingpin MORE (Mont.) said the party had a deep bench and would field a strong candidate.

"There is a talented pool of Nevada Democrats who are ready to step up to the plate, and we will recruit a top-notch candidate in Nevada who will be successful in holding this seat in 2016," said Tester in a statement.

The National Republican Senatorial Committee though said that, with Reid gone, the Nevada seat was their "top pickup opportunity."

"On the verge of losing his own election and after losing the majority, Senator Harry Reid has decided to hang up his rusty spurs," said NRSC Executive Director Ward Baker in a statement. 

"Not only does Reid instantly become irrelevant and a lame duck, his retirement signals that there is no hope for the Democrats to regain control of the Senate,” he added. “With the exception of Reid, every elected statewide official in Nevada is Republican and this race is the top pickup opportunity for the GOP."

— This post was updated at 9:48 a.m.