Two former Labour prime ministers have given their backing to Ian Murray to become the party's next deputy leader.
Both Tony Blair and Gordon Brown are supporting Labour's only remaining Scottish MP to succeed Tom Watson, after he stepped down in December.
But neither men have endorsed one of the three leadership candidates in the race to replace Jeremy Corbyn.
Mr Murray is facing competition from Angela Rayner, Dawn Butler, Richard Burgon and Rosena Allin-Khan.
Ms Rayner - Labour's shadow education secretary - is seen as the front runner in the race, after securing the most backing from unions, affiliate groups and constituency Labour parties.
But with ballots now dropping onto doorsteps, Mr Murray, shadow equalities minister Ms Butler, shadow justice secretary Mr Burgon and Tooting MP Ms Allin-Khan still have until 2 April to make their case before the vote closes.
The leadership candidates battling it out for the top job are shadow Brexit secretary Sir Keir Starmer, shadow business secretary Rebecca Long-Bailey and Wigan MP Lisa Nandy.
Both the new leader and deputy leader be announced at a special conference on 4 April.
In a video message backing Mr Murray for the post, Mr Blair said all the candidates were "wrestling with the inescapable fact that Labour's lost four times in a row" at general elections, and the party "has to be able to win power in order to put its principles into practice and to bring about real change in the country".
He said it was a "huge challenge" to face up to, but Mr Murray "gets it".
"Ian Murray understands that if Labour is to have any hope, it's got to be able to win in every part and every corner of the United Kingdom," Mr Blair added.
"It's got to have a bold vision and programme, but it's got to be a programme realistic enough to win power."
Mr Brown also said the candidate's "strong voice for Scotland will be a strong voice for the whole of the UK".
Meanwhile, Ms Rayner has spoken about her childhood in an interview with ITV News, describing how she had to care for her mother who had severe depression.
Appearing on camera alongside each other, her mother, Lynn Bowen, described how the MP was her carer when she was "in a very dark place".
During the interview, Ms Rayner also criticised Mr Corbyn, saying he did not "command respect" in the Labour Party, and describing herself as "more bombastic, more focused and more sharp".
Leadership race continues
Elsewhere, the leadership candidates are set to face another grilling at a hustings in Manchester later.
Sir Keir is viewed as leading the race after securing the most nominations to get onto the ballot paper, but there are still more than five weeks to go until voting closes.
Among those taking part will be 114,000 new members who have joined since December's election, where Labour won its lowest number of seats since 1935.
Members of affiliated trades unions and groups can also vote, as well as around 14,700 "registered supporters" who have paid £25 to take part on a one-off basis.
Earlier this week, Sir Keir, Mrs Long-Bailey and Ms Nandy all pledged to offer their rivals shadow cabinet posts if they are successful, and said they would happily serve in the winner's top team.