Senior Tories are playing down David Cameron's vow not to serve a third term as prime minister if he is re-elected.
Mr Cameron tipped Theresa May, George Osborne and Boris Johnson as possible successors in a BBC interview.
He was accused of arrogance by Labour - and pundits claimed the Tory election campaign would now be overshadowed by a battle for the party leadership.
But Mr Cameron's cabinet colleagues insisted he was simply giving a straight answer to a straight question.
Defence Secretary Michael Fallon said: "I think it was a fairly straight answer and it was a fairly obvious answer. He is not going to go on and on.
"There is a shelf-life to any politician. Nobody is absolutely indispensable."
Mr Fallon told BBC Radio 4's Today programme that people outside Westminster would not be interested in "what will happen in 2020".
'Humble and straightforward'
London Mayor Boris Johnson, who is bidding to return to the Commons on 7 May, in the safe Tory seat of Uxbridge, was quizzed about Mr Cameron's comments as he took a morning run.
"All he's saying is I think obvious and common sense, which is that he doesn't want to go on and on and on like Mrs Thatcher.
Timetable to 2020 - if Cameron wins general election
May 2015: General election. If David Cameron wins an outright majority he will serve a full five-year term
May 2016: Scottish Parliament and Welsh Assembly elections
2017: EU referendum. The outcome will decide Britain's future relationship with Europe. Mr Cameron plans to campaign to keep the UK in the EU but if he is on the losing side he may be forced to step down as Tory leader earlier than planned
May 2019: European elections. If he is still Conservative leader, David Cameron may wish to wait until after the European elections to step down, which would still give his successor time to bed in before the next general election
May 2020: General election
"But he's got five more years to complete the work of getting Britain's economic recovery on track, and there's still a lot to do, and he needs to make sure he's there to do it."
He later rejected claims that Mr Cameron was being "presumptuous," saying he was being "rather humble, straightforward and telling it like it is," adding that the comments were "no big deal".
Deputy Prime Minister Nick Clegg joked that he would "happily settle for two terms as prime minister" as he left the coalition government's final cabinet meeting before the election.
The Lib Dem leader would not be drawn on whether he thought Mr Cameron had made a mistake, saying: "I'm not going to start providing a running commentary on other people's comments about their own futures."
Interviewed in his kitchen by the BBC's deputy political editor James Landale, as part of series of profiles of party leaders, Mr Cameron said: "I've said I'll stand for a full second term.
"But I think after that it will be time for new leadership. Terms are like Shredded Wheat - two are wonderful but three might just be too many."
By James Landale, deputy political editor, BBC News
By answering my question, Mr Cameron has potentially opened a Pandora's box.
He has invited Westminster and the country to contemplate a time when he is no longer prime minister and that is a dangerous gamble to make so close to an election.
He is telling the voters that they can back him one last time in May and then they can see the back of him in five years' time.
But his opponents will say he is making an arrogant presumption about the election result, an assumption that he will have the choice over whether to serve a third term.
In a few weeks' time, the voters may make that decision a little earlier for him.
He added: "There definitely comes a time where a fresh pair of eyes and fresh leadership would be good, and the Conservative Party has got some great people coming up: the Theresa Mays, and the George Osbornes, and the Boris Johnsons.
"You know, there's plenty of talent there. I'm surrounded by very good people. The third term is not something I'm contemplating."
In response, a Labour source said: "It is arrogant and presumptuous of David Cameron to speculate about a third Tory term in 2020 before the British public have been given the chance to deliver a verdict on his first. The Tories are taking the British public for granted."
The Lib Dems said Mr Cameron was being "incredibly presumptuous". A UKIP spokesman said: "Mr Cameron's announcement will create the long-awaited civil war in the Conservative Party over Europe."
One of Mr Cameron's closest allies, Conservative Chief Whip Michael Gove, was the first to leap to Mr Cameron's defence, telling the BBC's Newsnight his comments were a "statement of the bleeding obvious".
He said: "One of the reasons that it will help us win is that it reinforces in everyone's mind the fact that we have, as our prime minister, a normal, sane, decent guy who is in politics for the right reasons, who when he is asked a direct question gives an honest answer and when he seeks public office does it because he wants to finish a job to make sure our economic recovery is sustained.
"He's not in it for glory, ego or wealth.
"He's in it because he believes that he has another five years to give and he has seen other leaders - including Tony Blair sadly - cling into office too long and therefore spoil the early promise that came with them into office."