This is an F-16 fighter jet.Since the 1970s, it's been a cornerstoneof the US Air Force.Now the US allows all these militaries to also have F-16s.And since Russia invaded Ukraine in 2022...Ukrainian President Volodymyr Zelenskyyhas been begging for them.“Zelenskyy has been doubling down on his request for...”“...NATO jets...”“...and they really are pleas for fighter jets.”But for Ukraine, the US hasn't been as generous.“You don't think he needs F-16s now?”“No, He doesn't needF-16s now.”And that might be surprising...because the US has already given nearly $47 billionin military aid to Ukraine over the past year.That's a lot of weapons.Far more than it gave even some of its closest allies in 2020...and more than four timeswhat it gave Afghanistan's army at theheight of the US-led war there.This is a historic number that you would see typically the US military give to another country over decades.The U.S. refusing to send F-16s is a choice worth understanding...because the weapons that the US has and hasn't chosen to send Ukraine and when they've sent themhave helped shape each phase of this war.So what has the US been giving to Ukraineand why?Back in 2014Russia took over Crimea and parts of eastern Ukrainewith the help of Ukrainian separatist fighters.In 2014, ragtag wouldn't even describethe state of the Ukrainian armed forces.This is Jack Detsch — Foreign Policy’sUS national security reporter.They'd been gutted by years of neglect.A lot of the troops didn't have uniforms.Some of them didn't have hot food.Ukraine's leaders asked the US for helpbut President Barack Obamaonly sent protective gear and supplies, not weapons.In 2018, President Donald trump agreedto send a limited number of anti-tankmissiles called Javelins.But the Ukrainian army was still woefully unpreparedif Russia decided to escalate the conflict...which it did.In 2022, Russia launched a full-scale invasion of Ukraine.Russian jets and missileswere doing immense damage from the air...and Russian tanks were pushing Ukraine's troops backwards.Ukraine again asked the US for help.From the beginning of the warthe Ukrainians wanted a lot of the things that you see on the menu right now.They wanted F-16s.They wanted main battle tanks.They wanted this stuff from the get-go.President Joe Biden agreed to send a large package of weaponsbut it mainly included the smallerand relatively unsophisticated kinds.The US sent more javelins, plus ammunition, gunsand even some anti-aircraft missilescalled Stingers.And many US allies sent similar types of weapons.Germany sent 1000 anti-tank missilesand 500 stingers.Belgium sent 2000 machine guns.But no one sent their advanced battle tanks or fighter jets.The main question in the beginning of the warwas not just what the US was going to send.I mean, the question was like, are these guys going to fight?Certainly that's been a resounding yes.Ukraine's soldiers used anti-aircraft missilesto prevent Russian aircraftfrom controlling the skies.And they used the guns, ammo, and anti-tank weaponsto halt Russia's progress.Like in this video, which shows Ukrainian soldiersdestroying dozens of Russian tanks approaching Kiev.But even though the Ukrainians were using these weapons wellthe US hesitated to send it more advanced equipment.So the UShas been concerned at almost every step about the potentialfor Russia escalating the conflict.The US worried that Ukraine might usesome of these advanced weaponslike fighter jets or long-range missiles to strike inside Russiasparking an escalation.This concern would come to define how the US supplied Ukraine.In the spring of 2022, the war entered its second phase.Russia and Ukraine's armies weren'tmoving as much anymoreand instead began pounding each otherwith artillery.Russia was firing a staggering 60,000 rounds a day...while Ukraine could only manage to fire around 6,000.And it was quickly running low.But the US was still hesitatingto expand the scope of its support.They're looking at what'skind of on the Christmas wish listand deciding what's actually prudent to give.Finally, in April 2022the US agreed to send Ukraine its own artillery.And like in the first phase of the wara number of allies then sent their own artillery...even though some had wanted to do it earlier.You sort of saw folks in Europe wanting the US to leadbut sometimes the US still very much deep in deliberation mode.The most important weapon the US sent were called HIMARS...powerful rocket launchers that could hit targetsas far as 80 kilometers.They weren't powerful enough to strike inside Russiabut they did enable Ukraine to hit Russian supply depotsand command posts far behind its front lines...which forced the Russians to move them backweakening its troops at the front.That's how Ukraine captured the Kharkiv regionin September and the major city of Kherson in November.And by then, a new phase was beginning.In winter 2023, both sides were planning new attacks.Russia was gearing upto push further into the Donetsk and Luhansk regions.But Ukraine also wanted to take back territory...particularly in the south.In order to do thisUkraine would need to move troops quicklywhich requires armored vehicles like tanks...something it had been asking for for months.Some countries had sent older models of tanks...but just like with artillery, the US waited.They wanted the Germans to act firstby sending Leopard battle tanks.The Germans...were waiting for the United Statesto give them some political top cover here.A little bit of a game of chicken.Finally, in January 2023the UK and then the US agreed to send their advanced tanks...prompting Germany and several allies to followwith their best battle tanks.Just like with anti-tank missilesand HIMARS before the US and its allies were hoping thatthese tanks can push Ukraine to winsome decisive victories in this phase...which is where we are now.If the Ukrainians kind of can't turn the tideturn the balance right nowit's going to be trickyto see how this doesn't go into an extended stalemate.That's why Ukraine is still asking for fighter jets.F-16s could protect Ukraine's tanks from Russian aircraft...making their attack much more powerful.Ukraine has also been asking the USfor a long range missiles called ATACMSwhich it could use to strike Russian positions as far as 300 kilometers behind their lines.Already, a few allies are in favor of sending these weapons.But as of this videothe US is hesitating over familiar concerns.Questions about their readiness for training on those.Also, of course, you know, just the question again...how far are the Ukrainiansgoing to fire these things?So far, none of the decisions to send any of these weaponshas inspired Russia to escalate.And in March, Polandand Slovakiaagreed to send some of their older fighter jetsmaking the eventual approval of F-16sor long range missiles more of a possibility.But after giving Ukraine over $46 billion in military aidpublic opinion in the US is changing.A recent Pew Research poll showedthe proportion of people who believe the UShas sent too much aid to Ukraine has grownparticularly on the right.Biden, facing a lot of pressurenot only within his party, but, of coursefrom Republican rivals getting ready for the 2024 debate stage.That's going to make it much more difficultfor President Bidento sustain this clip.And even if Biden maintains popular support to send weaponshe might not have enough.A recent analysis found that certain suppliesmay be approaching the minimal level that the US requires for its own war planning.It's why the US is now focusing on ways to increase production of weaponsat homein allied countriesand in Ukraine.But just building those plants could take years.One year of US and allied supporthas helped transform the Ukrainian armyinto a formidable forcewhose soldiers have repeatedly heldits ground against a much larger Russian army.But with both the battlefield and US politics changingthe questions now are how well is Ukraine going to fightwith what they haveand how much more US help can they count on?Thanks for watching this episodeof Vox Atlas.Vox has been covering the war in Ukraine since it beganwith in-depth explainers and analysis.You can find all our coverage of the war at Vox.com/Ukraine.