In her opening pitch, the shadow business secretary pledged to champion “progressive patriotism”, while avoiding criticism of the outgoing leader or of his handling of the antisemitism issue.
But, in evidence that doubts are growing on the Left about her credentials, party chairman Ian Lavery also announced that he is weighing up a leadership bid.
“He has had a tremendous amount of support and is seriously considering all of his options,” said a spokesman for the former miner, a close Jeremy Corbyn ally.
Ms Long Bailey was immediately installed as favourite by some bookmakers, when Labour’s catastrophic election defeat triggered Mr Corbyn’s intention to stand down.
Long cultivated by the leadership as his likely successor, she then said nothing for more than two weeks, allowing criticism to grow that she would be unable to break free of his legacy.
Now, in an article for The Guardian, the Salford MP has partly blamed rows over the EU for Labour’s defeat, saying: “The country was sharply divided by Brexit and our compromise solution satisfied too few.”
But she added: “We can’t blame Brexit alone and we must recognise that it’s no good having the right solutions if people don’t believe you can deliver them.”
Ms Long Bailey also, like Keir Starmer, insisted the radicalism Corbyn brought is here to stay, writing: “Strategies designed in Westminster were partly to blame, but it’s also true that Labour’s support has been falling in many communities for a decade or more.
“We must rebuild trust, not only in our party but in the idea that change really is possible.
“This means we cannot return to the politics of the past. Our transformative agenda is principled and popular, while triangulation and soft pedalling will only take us backwards.”
Some voters viewed Mr Corbyn as unpatriotic, because of his pacifism, his reluctance to sing the national anthem and his failure to immediately challenge Russia over the Salisbury poisonings.
Ms Long Bailey wrote: “From ex-miners in Blyth Valley to migrant cleaners in Brixton, from small businesses in Stoke-on-Trent to the self-employed in Salford, we have to unite our communities.
“Britain has a long history of patriotism rooted in working life, built upon unity and pride in the common interests and shared life of everyone.
“To win we must revive this progressive patriotism and solidarity in a form fit for modern Britain.”
Labour’s ruling national executive committee will meet next Monday to decide the format of the election, with the intention of installing the new leader by the end of March.