That's a big “if,” given the PM's knack for doubling down on declarations that fail to survive the first contact with reality.
Tory leader Kemi Badenoch seized on this fragility, hammering the PM on Chancellor Rachel Reeves' stewardship of the economy during PMQs.
She didn't hold back, accusing Labor of saddling the UK with “fewer jobs, lower growth and higher borrowing costs”.
Ms Badenoch knew exactly how Mr Starmer would defend himself. The same way he always does. By blaming Tory profligacy and seeking refuge in that £22billion black hole they allegedly left behind.
She virtually begged him not to go there again. Or pin Labour's errors on “global factors”.
Starmer predictably did both.
First, the global economy took its share of the blame. Then he dived straight into his black hole.
This has become a handy hiding place for Labour, allowing them to deflect any question about their own culpability.
Starmer then started banging on about how Labor is building growth and stability, even though it's doing the exact opposite.
As he rallied to Reeves' defense she sat stiffly by his side, looking like the zombie Chancellor she has become.
As Starmer batted away Ms Badenoch's questions, she started smiling and nodding as if her job depended on it.
Which of course it did.
Then Starmer decided to go all-in, declaring Reeves would stick to her promise of holding just one budget a year. Presumably in the Autumn.
He doubled down by claiming – despite all the evidence – that she was in no danger of breaking her “non-negotiable” fiscal rules.
That's two huge hostages to fortune, right there. You could practically hear the sniggers in the city.
Starmer is in no position to make these promises. If UK borrowing costs continue to rise, the extra interest charges will propel Reeves head first through her unbreakable fiscal rule.
And if that happens, she'll have no choice but to hike taxes or cut spending in an emergency spring budget.
If she hasn't already resigned.
That's the problem when you lose control of the economy. You don't decide important matters like these anymore. The bond market does it on your behalf.
Starmer also insisted that Reeves had his “full confidence” and would remain Chancellor for the entire term of this Parliament.
Five years has never felt so long.
Cheer up though, it's unlikely to happen. Once a PM declares a chancellor has their full confidence, they never last long.
It's yet another Starmer pledge that won't survive contact with reality.
If the fiscal turmoil worsens, Reeves could be gone in weeks, or even days. Bond markets will demand it. And as Liz Truss learned, they don't take prisoners.
Reeves was laughing by the end, but the night sweats will surely follow.
The more Starmer insists something is true, the less people believe him. Bitter experience, I suppose.