Europe's leaders are scrambling. Their hastily convened security summit in Paris on Monday is proof of that.

They are still reeling from not being invited by the US to talks with Russia over the future of Ukraine. US President Donald Trump said on Sunday he could be meeting Russian President Vladimir Putin "very soon".

Can Europe, under pressure, put political differences and domestic economic concerns aside, and come up with a united front on security spending and on Ukraine's future, including potentially sending troops there - to force themselves a spot at the negotiating table?

They are going to try.

On Monday morning, UK prime minister Sir Keir Starmer said the UK was "ready and willing to put troops on the ground". Even in Germany, ahead of a heated election, the foreign policy spokesman of the CDU party, expected to win the most seats, said Europe's largest country would also be willing to commit troops within an international framework.

The Trump administration is clearly not 100% sure what it wants to do about Ukraine. There were a number of mixed messages over the weekend.

This allows Europe a tiny window of opportunity to try to persuade the American president it's an invaluable partner.

It hopes to do that via this Paris meeting, getting the ball rolling on two major issues demanded by Donald Trump: That Europe spend and do more for its own defence, and that Europe send troops to Ukraine after a ceasefire.

Europe's leaders insist Kyiv be directly involved in ceasefire talks too. They've long maintained the view that "there can be no decisions about Ukraine, without Ukraine".

But it's about even more than that for Europe.

It is the cold realisation - much dreaded, but not entirely unexpected - that the Trump administration does not prioritise relations either with European partners, or their defence.

Europe has relied on a security umbrella provided by the US since World War Two.

Depending on the parameters of the Russia-US talks over Ukraine, and how emboldened Putin feels by them, there is also a European fear this could end up changing their continent's security architecture.

Putin historically resents the spread of Nato eastwards. Russian neighbours - the tiny, former Soviet Baltic States and also Poland - now feel particularly exposed.

Not all European countries will be at Monday's summit. Just those with military heft: the UK, France, Germany, Italy, Poland, Spain and Denmark - which is expected to represent the Baltic and Nordic nations, plus the EU Council president and the secretary general of the defence alliance, Nato.

Other countries will reportedly have later, follow-up meetings.

Even at the small Paris gathering, it will be hard, if not impossible, to agree concrete defence spending increases. Poland plans to spend 4.47% of its GDP on defence in 2025. The UK is struggling towards, and hasn't yet reached, 2.5% of its GDP.

But leaders can pledge to coordinate better, spend more inside Nato and shoulder most of Ukraine's post-war reconstruction. The EU is expected to bolster its defence effort too.

A large part of the Paris meeting will also focus on the question of sending troops to Ukraine after a ceasefire.

The idea being discussed is not for peacekeeping troops but rather a "reassurance force", stationed behind, rather than on, any eventual ceasefire line.

The aim of a European troop presence would be three-fold. To send a message to Ukrainians: that they are not alone. Another message to the US, to show that Europe is "doing its bit" for defence of its own continent, and the last message to Moscow, to warn that if it breaks the terms of an eventual ceasefire, it won't be dealing with Kyiv alone.

But it's a controversial concept and may not be popular with voters. In Italy for example, 50% of people asked don't want to send any more weapons to Ukraine, never mind sending sons and daughters, sisters and brothers there.

There are so many as yet unanswered questions:

How many troops would each European country have to send, for how long, and under whose command? What would their mission statement be - for example if Russia broke the terms of an agreed ceasefire, would that mean European soldiers would be directly at war with Russia? Would the US have their back if so?

Europe would want a US security guarantee before deploying soldiers to Ukraine. It may not get one.

It's far too much to be decided on Monday. And leaders, including UK Prime Minister Keir Starmer, come to Paris with their own domestic concerns - can they afford extra defence spending, do they have the troops to send to Ukraine?

Richard – now Lord – Dannatt is the former head of the British Army. He told the BBC that the UK military is too depleted to provide a significant proportion of troops for Ukraine. He said around 100,000 troops would probably be needed in total and the UK would be expected to provide a considerable number of those. The British Army insists it has earned a worldwide reputation for excellence.

But this summit is more broad brushstrokes than fine print. The conversation can at least get started publicly.

Will Donald Trump be paying attention?

Hard to know.

There's talk of sending an envoy to Washington after the Paris meeting to make Europe's case. Italy's Prime Minister, Giorgia Meloni, is close to the Trump administration, for example.

Sir Keir Starmer has a planned visit to Washington in a few days. This could be his chance to act as a bridge between Europe and the US.

The Paris meeting also offers an opportunity for the UK and other European leaders to further mend relations after the bitterness of Brexit.

Mark Leonard, head of the European Council on Foreign Relations, notes that Starmer could "demonstrate that Britain is a responsible stakeholder for European security ... Something that will be noticed and translate into goodwill when it comes to negotiations on other issues".

Issues like trade relations and law enforcement co-operation which the UK hopes to improve with the EU going forward.

Host nation France is feeling confident. President Macron has long advocated that Europe be less reliant on outside countries for supply chains, tech capabilities and very much so when it comes to defence. He made headlines a year ago by first mooting the idea of troops on the ground in Ukraine.

France is "fiercely proud" that its intelligence and security services are not intertwined with the US, unlike the UK, says Georgina Wright, deputy director for international studies at the Institut Montaigne. That makes it less complicated to untangle, now that Trump is in the White House, demanding that Europe take care of itself.

The US has sent a document to European allies consisting of six points and questions, such as which countries would be willing to deploy troops to Ukraine as part of a peace settlement, and which governments would be prepared to increase sanctions on Russia, including more strictly enforcing existing ones.

But Julianne Smith, until recently the US ambassador to Nato, says this kind of complicated diplomatic work normally takes weeks of meetings and can't be organised by filled-in forms.

She adds that whatever Europe's leaders achieve in Paris, if they use that to demand a seat at the negotiating table over Ukraine, their hand is weak.

"If Trump blinks and says no, does Europe refuse to help altogether? They can't cut off their nose to spite their face."

Essentially, if the US plans to turn away from Ukraine and from Europe more broadly in terms of security, they will have to significantly up their defence game anyway.

If Donald Trump isn't watching, Vladimir Putin certainly is.