Thursday's agreement in Minsk was welcomed by the White House, with Press Secretary Josh Earnest saying in a statement that it represented "a potentially significant step toward a peaceful resolution of the conflict" and praising the "tireless efforts" of Angela Merkel and Francois Hollande.

But as State Department spokesperson Jen Psaki acknowledged to reporters, "the proof is in the pudding." She continued, "A piece of paper is just a piece of paper until it's implemented," and warned that there was evidence that Russia was continuing to take "aggressive actions." This amid reports from officials in Kyiv claiming that 50 Russian tanks had crossed the border into Ukraine even as the talks were ongoing.

Skepticism on substance

After the failure of the first Minsk agreement, there is skepticism across the board in Washington that this time will be any different. Many are also voicing doubts about the substance of the new deal. Former US Ambassador to Ukraine John Herbst told DW: "It's certainly not a very good agreement for Ukraine." Herbst highlights what he sees as a key shortcoming with the deal: that Ukraine will not gain control of its border with Russia until the end of 2015, preventing it from halting the alleged inflows of Russian personnel and weapons.

Herbst lays the blame for this partly at the door of France and Germany. "My understanding - I can't say this for certain - is that the Western allies were willing to consider an even longer period of time. Which would suggest that they weren't as supportive of Ukraine - the victim in this - as perhaps they could have been."

Jeremy Shapiro of the Brookings Institution is less critical. He told DW that without the deal, Ukraine's prospects of controlling its border would have been even dimmer. And he welcomed the agreement as offering potential “breathing space” for further talks.

The debate over arms

The diplomatic flurry in Europe that led to the new Minsk agreement came just as the mood in the US was heading in the opposite direction - driven by a major report co-authored by Ambassador Herbst and seven other senior former diplomats, policymakers and military leaders. It argued that the US should provide Ukraine's beleaguered military with lethal defensive weapons - going beyond the communications equipment, night goggles and other gear it has already been supplying.

The report argued that the West's tools of diplomacy and sanctions were failing to prompt a Russian backdown in Ukraine - and that a stronger deterrent was needed: "Only if the Kremlin knows that the risks and costs of further military action are high will it seek to find an acceptable political solution."

It's an argument that is being taken seriously in the White House. Barack Obama confirmed he was considering such a move when he hosted Angela Merkel in Washington ahead of the Minsk talks. This added to fears of a rift in the Western approach to the Ukraine crisis, given Merkel's belief that arming Ukraine would only escalate the conflict.

Good cop, bad cop?

Ambassador Herbst downplays the risk of such a rift, arguing that "Unity can allow for certain differences of approach without being destroyed. And that's very bad news for Putin."

Amid talk of the US and the EU adopting good-cop/bad-cop roles towards Russia, Herbst says the debate over arming Ukraine may have even spurred Merkel and Hollande into diplomatic action: "It may be that they were thinking about it before all the talk in Washington began. You can't rule it out. But they didn't announce it until after our report was issued and you had this flurry of activity. So that does suggest there's a connection." Herbst also argues that the threat of Ukraine receiving US arms may have helped encourage Putin to sign up to the Minsk agreement.

Jeremy Shapiro of Brookings was one of the most vocal critics of Herbst's report. He told DW he's unpersuaded that the debate had a positive impact: "It's also likely that it had some role in the escalation that we saw in the last few days and weeks." He continues: "Fundamentally, this problem doesn't get solved by trying to inject Washington debates into a dynamic and confusing situation. Fundamentally it gets solved by the parties on the ground and their power balances."

The long term

Both Herbst and Shapiro agree that the new Minsk agreement is likely to rob the debate over arms of some momentum - but both suspect it will be back, given their shared skepticism that Minsk will mark a clean end to the violence. Should the crisis take another turn for the worse, they agree the political pressure on Barack Obama to back arming Ukraine will rise significantly.

For Herbst, the pressure will be overdue: he has long argued for a tougher line against Russia. As he put it to DW, "Ukraine vis-à-vis the Kremlin is in a weak negotiating position. Ukraine strongly defended by the West - sticking up for the principles of sovereignty, territorial integrity and not changing borders by force - would be in a less weak position."

Shapiro counters that the Washington foreign policy establishment is ignoring what he says is the underlying issue: "How to treat the nations between the EU and Russia. It is fundamentally a question of Russia's perception that the West is coming to get it, and is using these countries as a road to overthrowing the Russian regime."

Shapiro says the West has to confront this perceived threat - even if it sees it as unfounded: "Even if Russia is a paranoid schizophrenic, it's a paranoid schizophrenic with 8,000 nuclear weapons. We simply have to deal with it."