Reading between the lines
Is she fooling herself? Or does Theresa May have reserves of political magic as yet unseen?
On paper her position looks as unpalatable as any prime minister's in modern times.
A negotiation against 27 other countries, some of whom want to make the UK pay. A deal of mind-bending complexity beckons. A wafer thin majority in Parliament. The Scottish government intent on pushing for a vote to break up the other union.
All this, knowing that one false move could wreak havoc on the economy or unleash demons inside her own party.
And yet perhaps, after the clamours of the campaign, the political traumas and triumphs of recent months, the moment for firm but polite pragmatism has arrived. The tone of her letter today showed she feels the need to persuade the rest of the EU that she wishes them no harm, revealing she is well aware that she knows it will be difficult to get them on side.
There are hints between the lines that she is conscious too she will need to compromise. The response from the rest of the EU today provides a glimpse of how much resistance she is bound to face.
Yet her choice to emphasise the security risks of no deal displays that she will not just play nice. To put security on the table as part of any negotiation is a controversial choice.
Even though it is certainly not the first time that Theresa May has raised the issue, there's been pushback at her decision to put arrangements that could affect the safety of Europeans everywhere on the agenda so prominently.
One cabinet minister told me tonight though that there was no intention for this to be an "ultimatum" but "these are our strengths, these are our cards" - we should not be surprised if the prime minister chooses to play them.
Close confidants say of Theresa May she is fearless in pursuit of what she wants. Her approach to seemingly insurmountable problems is to keep working, keep searching for solutions.
But just as determination can go a long way to achieving any goal, politicians can be resolute and also wrong.
There are no guarantees that the prime minister's aims are the right ones for the country. Still less certainty that they can be achieved.