Before the Ukraine discussions, the US and Russia have a lot of disagreements.

Following a frank discussion between Presidents Joe Biden and Vladimir Putin over Russia’s army buildup near the Ukrainian border, both parties said they are confident that a route to lowering tensions will emerge at diplomatic talks scheduled for January.

However, with less than two weeks until senior US and Russian officials meet in Geneva, the divide is wide and the likelihood of resolving the issue is fraught with difficulties.

Biden told reporters on Friday that he informed Putin over the phone the day before that the impending talks would only succeed if Putin “deescalated, not inflamed” the situation in the days ahead.

The US president said he also wanted to make it clear to Putin that if Russia invaded Ukraine again, the US and its allies would be ready to retaliate with harsh sanctions.

“I told President Putin that any more steps into Ukraine would result in serious consequences,” Biden stated. “With NATO allies, we will enhance our presence in Europe.”

Meanwhile, Biden’s national security staff focused on preparations for the Geneva talks, which are scheduled for January 9 and 10 and will address Russia’s massing of 100,000 troops on its border with Ukraine.

The Geneva discussions will be followed by Russia-NATO council talks and a meeting of the Organization for Security and Cooperation in Europe, which will be led by senior State Department officials on the US side.

Biden is set to speak with Ukraine President Volodymyr Zelenskyy over the phone on Sunday. According to the White House, the two leaders will discuss preparations for upcoming diplomatic engagements.

Secretary of State Antony Blinken met with Canadian Foreign Minister Mélanie Joly, Italian Foreign Minister Luigi Di Maio, and NATO Secretary General Jens Stoltenberg on Friday to debrief them on the Biden-Putin chat and discuss summit preparations.

“The next two weeks are going to be difficult,” said Daniel Fried, a former US ambassador to Poland who advised Presidents Barack Obama, George W. Bush, and Bill Clinton on Eastern Europe.

“The Biden administration has done a good job of laying out and framing the negotiations.” But the most difficult test is still to come, as Putin will continue to threaten and play chicken with us to see how committed we are.”

While Biden underlined his readiness to impose penalties that would echo throughout Russia, Kremlin officials warned Biden against making a “colossal blunder” that would have far-reaching consequences for the already strained US-Russian relationship.

On Friday, a top Putin aide reiterated that Russia will not back down from its demands for written security guarantees. Moscow wants it written into law that any future NATO expansion must exclude Ukraine and other former Soviet bloc countries, and the bloc must remove offensive armaments from countries in Russia’s immediate vicinity.

“We will not allow our actions to be drowned in lengthy talks,” Foreign Minister Sergey Lavrov said on Friday, according to the Russian state news outlet RIA-Novosti. “If no constructive response is received in a fair time and the West continues on its aggressive path, Russia will be forced to take all necessary steps to maintain a strategic balance and eliminate intolerable risks to our security.”

The Biden administration, as well as NATO allies, have made it clear that Russia’s demands will not be met.

Some in Washington have questioned how productive conversations may be because of the obviously unrealistic tone.

Following the Biden-Putin call, a group of 24 former US national security officials and Russia experts — including officials from the Obama, George W. Bush, and Clinton administrations — issued a statement calling on Biden to immediately and publicly lay out the sanctions that Russia would face if it pursued military action.

Several former US ambassadors, including Fried, Russia envoys Michael McFaul and Alexander Vershbow, and Ukraine envoys Steven Pifer and John Herbst, signed the statement.

“We believe the US should take prompt actions to influence the Kremlin’s cost-benefit calculations before the Russian leadership opts for further military escalation,” the group stated, “in close cooperation with its NATO partners and Ukraine.”

“If Russia attacks Ukraine, such a reaction would involve a package of large and harsh penalties that would be implemented immediately.” The outline of these sanctions should ideally be given to Moscow immediately, so that Moscow is aware of the scale of the economic impact it would face.”

The Russians, for their part, continue to argue that Ukraine poses an existential threat to them.

Lavrov charged on Friday that “the Kyiv government inevitably views this assistance as a carte blanche for the use of force,” citing a rise in weapons sales to Ukraine and the increased frequency and breadth of joint military drills undertaken by Western nations with Ukraine. He also stated that Russian people in eastern Ukraine will be protected.

“Russia will take all necessary measures to safeguard residents of Donbas, where hundreds of thousands of our citizens dwell,” he stated. “Any possible military provocations by Kyiv against Donbas will be met with a sufficient response.”

It would be a mistake for the White House to let “Russia unilaterally dictate the agenda,” according to Simon Miles, a diplomatic and international Cold War historian at Duke University.

“Whatever the US can do to keep the Russians on the back foot, rather than allowing the Kremlin to define the agenda,” Miles said, “is going to be critical to getting a good settlement.”