(CNN) — Russia’s mass mobilization, looming offensive and missile-borne terror against civilians is triggering fresh calls for even greater Western lethal aid to Ukraine, days after leaders signed off on their latest package that included the first tanks.

A building public debate over whether to send F-16 fighter jets is resurfacing a dilemma underlying the entire NATO response: Is the aim of the United States and its allies simply to allow Ukraine to ensure its survival or is it to help it expel Russia from all its territory and to ensure the defeat of Russian President Vladimir Putin?

The likely escalation in the war, close to its first anniversary, comes as Ukrainian President Volodymyr Zelensky warns that Moscow is mustering its forces for a “revenge” attack against the free world. The sense that another turning point is approaching was, meanwhile, underscored Thursday by CIA Director William Burns. “The key is going to be on the battlefield in the next six months, it seems to us,” Burns said at Georgetown University. This involves “puncturing Putin’s hubris, making clear that he’s not only not going to be able to advance further in Ukraine, but as every month goes by, he runs a greater and greater risk of losing the territory he’s illegally seized so far,” the CIA chief said.

Washington is hearing Ukraine’s calls for even more multi-billion dollar assistance. It is about to announce a new $2.2 billion haul that includes longer-range missiles for the first time, according to multiple US officials. CNN’s Kevin Liptak and Oren Liebermann reported that the Ground-Launched Small Diameter Bomb – a guided missile with a range of 90 miles – will be included in the package. It could take weeks or months for the weapon to arrive, however, since the US will contract with American arms manufacturers to provide it.

Still, the latest US offering solidifies one of the most important and ironic consequences of the war. One of Putin’s perceived invasion goals was to forever sever the hopes of Ukraine, which was once part of the Soviet Union, of joining NATO. It may not be a member of the alliance, but Ukraine is now waging a stronger-than-expected response against Moscow using some of the West’s most advanced military kit.

Ukraine wants more

Judging by the comments from senior Ukrainian government figures in the last few days, the government in Kyiv still doesn’t believe it has the military capability to achieve the kind of change to Putin’s mindset that Burns is describing.

This is despite the decision last month by NATO leaders to send more than 300 battle tanks to the war, including British Challengers, German-made Leopards, and eventually the advanced American M1 Abrams machine. For example, Ukrainian Defense Minister Oleksii Reznikov told NPR this week that he was optimistic the US and its allies would eventually supply his country with fighter jets including F-16s, which President Joe Biden has consistently said he isn’t sending. “What is impossible today is absolutely possible tomorrow,” Reznikov added.

The question of whether to offer Ukraine jets is complicated. It requires an evaluation of whether there is a military need for the aircraft and a role they could properly fill. The US and allied leaders must balance the impact the aircraft could have with the risk of further escalating a fraught Western standoff with Putin. Leaders might also need assurances from Ukraine that the aircraft would only be used for operations inside Ukraine, in order to avoid widening the war into Russia. Out of similar concerns, the new package will not include the ATACMS missile that Ukraine wants, which, with a range of over 200 miles, could be used to target Russian soil, CNN reported.

There’s no sign that Ukraine will be getting F-16s soon. “No,” Biden said when asked this week whether the US would offer the jets to Ukraine. British Defense Minister Ben Wallace said that at least for now, it wasn’t the right time to send the aircraft. “What they need right now is armor and tanks,” Wallace said, though he left Kyiv with some hope when he said, “Never rule anything in and never rule anything out.”

The question of the military usefulness of F-16s comes up against concerns that they might prove vulnerable to still effective Russian air defenses and aircraft. CNN’s Mick Krever reported this week that for the F-16s to be a game-changer, Ukraine would first have to destroy Russian air defenses and establish air superiority over the battlefield. The jets might be most useful as a defensive weapon for the military and be better at shooting down Russian missiles, for instance, rather than for close air support missions near the frontlines, Krever wrote.

Evelyn Farkas, a former US deputy assistant secretary of defense, however, told CNN Wednesday that she was hopeful that US reticence to allow fighter jets into Ukraine – mirrored by an earlier refusal by Biden to allow Poland to transfer Soviet-era MiGs earlier in the war – would recede and that F-16s could be sent.

“The Russians have air power or they have essentially power that they can employ through the air. And I think this is what’s missing for the Ukrainians,” Farkas said.

“I think we need to provide the Ukrainians with aircraft so that they can provide cover for their troops on the ground.”

NATO united, for now

One rationale for not sending the jets is that they would require fresh and intensive training for pilots reared on former Soviet-era aircraft. Some Western experts discount Ukraine’s contention that the planes could be used with their pilots with a minimum of training and argue that if the war has a critical six-month time frame approaching, the aircraft could arrive too late anyway.

Still, the idea that sophisticated Western weapons are too complex for Ukrainian armed forces – or that it would too long to train soldiers how to use them – is a familiar one. There’s been a pattern of initial US reluctance to offer Ukraine systems like Howitzers, Patriot anti-missile missiles and Abrams tanks, which has been overturned by the pressure of events in the war.

And Zelensky, who has operated an effective public relations campaign in the West since the Russian invasion nearly a year ago, dismisses the idea that his forces, who have heroically resisted Russian might, will not be able to quickly get up to speed on weapons. “I assure you that Ukrainian soldiers can perfectly operate American tanks and planes themselves,” he said during his address to a joint meeting of Congress in December.

Several European leaders, including Dutch Prime Minister Mark Rutte and French President Emmanuel Macron, have declined to rule out sending fighter jets, and Polish Prime Minister Mateusz Morawiecki said in an interview with German daily newspaper Bild that if the whole of NATO agreed, he would favor sending fighter jets. But there is no sign that such a step is imminent. The transfer of US-made jets would require the agreement of Biden.

And all of the NATO leaders have appeared determined to show unity over jets in the wake of Biden papering over a rift with Germany last month, when he agreed to transfer the tanks to Ukraine.

Meanwhile, Putin is reacting to fresh momentum in the dispatch of arms to Ukraine with a familiar tactic – veiled threats to Western powers that he could use small-yield tactical nuclear weapons in the war.

“We are not sending our tanks to their borders, but we have something to answer with. And it will not end with the use of armored vehicles,” the Russian leader said during a visit to Volgograd to mark the 80th anniversary of Soviet victory in the Battle of Stalingrad.

Putin’s threats haven’t deterred Western nations before as they get drawn ever deeper into what is in effect a proxy war with Russia in Ukraine. But his comments will again fuel fears that pouring weapons into the war will only escalate it and risk its spread.

Burns argued, however, that Putin made a bad bet that he can grind down Ukraine while political fatigue takes a grip on Europe and the US.

The CIA chief said he told one of his Russian counterparts, Sergey Naryshkin, in November that “that Russian calculation is as deeply flawed as the original decision to go to war last Feb. 24 was.”