This is the kind of reset button Vladimir Putin will understand. James Mattis went to Ukraine on their independence day and pledged to strengthen ties between Washington and Kyiv, even as far as supplying defensive weapons for threats on their borders … or perhaps more pointedly, within them. Mattis also ended any speculation that the Trump administration would consider Russia’s annexation of the Crimea as a fait accompli, saying the US “will not accept” the peninsula’s seizure.

Most pointedly, Mattis pledged to Petro Poroshenko that US sanctions on Moscow will remain in place until Russia backs down:

On the 26th anniversary of Ukraine’s independence from Moscow, U.S. Defense Secretary Jim Mattis accused Russia of menacing Europe and suggested that he favors providing Ukraine with defensive lethal weapons.

Mattis also said the Trump administration will not accept Moscow’s annexation of Ukraine’s Crimea region.

After attending a spirted and colorful independence day parade, Mattis met with President Petro Poroshenko and other top government leaders. He is the first Pentagon chief to visit the former Soviet republic since Robert Gates in 2007.

“Have no doubt,” Mattis said at a news conference with Poroshenko. “The United States stands with Ukraine.” He said Washington does not, “and we will not,” accept Russia’s annexation of Crimea, a 2014 action that was followed by Russian military intervention in support of separatists in eastern Ukraine.

The comment on sanctions and the choice of venue in particular are calculated to get Putin’s attention. The suggestion from Mattis that the US might consider shipping lethal arms to Poroshenko is calculated to get Putin to stop violating the Minsk agreement. This option has been under discussion for a while, but it’s the first time that a senior member of the administration’s national-security team has gone on record to endorse it, albeit conditionally:

Mattis also played down fears, voiced by the previous White House administration under Barack Obama, that supplying weapons could escalate the situation.

“On the defensive lethal weapons, we are actively reviewing it, I will go back now having seen the current situation and be able to inform the secretary of state and the president in very specific terms what I recommend for the direction ahead,” Mattis said.

“Defensive weapons are not provocative unless you are an aggressor and clearly Ukraine is not an aggressor since it is their own territory where the fighting is happening,” Mattis said.

Poroshenko said he was “satisfied” with the progress on discussions about weapons, and also said he and Mattis had discussed the possibility of a U.N.-backed armed force being sent to eastern Ukraine.

That would be unlikely in the extreme. Dispatching an armed peacekeeping force would require a UN Security Council resolution, and Russia would veto it under any circumstances. Putin’s still seething about the breakup of the Balkans and especially the independence of Kosovo at the expense of his Serbian allies, accomplished as a fait accompli of its own by a NATO peacekeeping force.

Senator John McCain had urged the arms sales yesterday:

“It is long past time for the United States to provide Ukraine the defensive lethal assistance it needs to deter and defend against further Russian aggression,” McCain said in a statement.

[“]Raising the cost of aggression may help to change Vladimir Putin’s calculus, pressure Russia to fully comply with the Minsk agreements, and, ultimately, create more stable security conditions on the ground that are essential for peace.”

He may get his wish, or Putin might head it off by pulling back on his Minsk-pact violations as a way to forestall it. Either way, Mattis is signaling that the Trump administration may talk about better relations with Putin, but that they will demand that they come on American terms. Poroshenko has to be breathing a sigh of relief after this visit, especially after his government’s connections to the DNC during the election became a sore point for Trump and his team in the Russia-collusion narrative.