The slow trickle of US aid and restrictive Biden administration policies have forced Ukraine onto the “back foot” in its fight against Russia — as the enemy forces continue their unrelenting push into Ukrainian territory near Kharkiv, the second-largest city in the country.

“Right now, the Russians have the initiative across the entire theater. They’re dictating the place, the time, the intensity and the tempo of military operations,” George Barros, the Institute for the Study of War’s Russia team lead told The Post.

“The Ukrainians are on the back foot and are forced to react.”

The Biden administration just announced it would send an additional $275 million in aid to replenish Ukraine’s supply of “urgently needed” weaponry, such as rockets and artillery rounds — but it could be too little, too late.

The latest package is the fifth tranche of aid for Kyiv since Congress approved a $60 billion supplemental package last month, however, as US lawmakers debate the bill, it choked off the flow of weapons to the region for months.

That delay has been costly, forcing Ukraine to cede additional territory while creating a crisis of morale for the country’s volunteer armed forces.

“This time last year there was no problem with Ukrainian manpower. There were volunteer drives where men were signing up in huge numbers. They were coming off successful counteroffensives in 2022 and received new equipment from the West in early 2023. Morale was high and things were hopeful for the future,” Barros said.

But things look very different today after a series of setbacks on the battlefield and the slow response by Congress to approve more aid.

“[Ukrainian forces] feel abandoned. Morale is low, they don’t feel supported. They know DC is constraining their ability to defend themselves,” Barros said.

“They’re not enthusiastic about going to fight because they understand there are materials shortages, so there’s no guarantee they’ll be equipped, armed, and trained properly.”

Even though Congress finally passed the supplemental package, American equipment has been slow to reach the front lines at scale, spreading Ukrainian forces thin as they make the most of already constrained resources.

Russia was well aware of both this delay, and likely timed their advance on Kharkiv to start on May 10 because it was after the aid package was passed but before equipment started to reach the front.

Barros said Russia pressed ahead with the operation even though they had only amassed half of their desired 60,000-100,000 troops, “because if they waited a couple more weeks then the Ukrainian situation would be more stable.”

Even when US arms and munitions shipments finally reach Ukraine in greater numbers, it is unlikely to be enough to enable the country to launch effective counteroffensives against Russia.

“The tactical situation will improve for the Ukrainians, but the operational situation I don’t think is going to improve barring significant policy changes,” Barros said, pointing to restrictive rules of engagement that prohibit Ukrainian forces from striking at Russian forces from within Russia.

“I remain hopeful that Washington undertakes a course correction.”

Fully aware of this limitation, Russia has positioned its weaponry and forces just across the border from Ukraine, bringing them close to within artillery range of Kharkiv without fear of being attacked.

“One way the US can blunt the Russian offensive and help the Ukrainians seize the initiative is to change the rules of engagement for America-provided weapons,” Barros said.

Olexsandra Ustinova, head of Ukraine’s paramilitary commission on arms and ammunition, recalled an instance where they spotted Russian forces “sitting one or two kilometers from the border inside Russia” but that “there was nothing we could do about it,” The Times reported.

Ever since US weapons began flowing into Ukraine, the country has been bound by an agreement that it would not fire them into Russian territory, a restriction put in place over the Biden administration’s fears the war could escalate into World War III.

Slowly but surely, cracks have started forming in the prohibitive policy.

Ukrainian President Volodymyr Zelensky said in an interview with the New York Times this week that his country not being allowed to launch US-made artillery into Russia gave its military rival a “huge advantage.”

The second-guessing of the hamstringing policy has even reached the US State Department.

After a recent trip to Kyiv, Secretary of State Antony Blinken has started pushing the administration to back off the policy, the Times reports.

However, the outlet said Blinken’s proposal was still “in the formative stages” and it was unclear whether Biden would be on board.

Former Under Secretary of State for Political Affairs Victoria Nuland, who left the department in March, said in an interview on ABC’s “This Week” Sunday that striking offensive targets over the Russian border “ought to be fair game,” particularly after Russia escalated hostilities with its assault on Kharkiv.

“It’s important to get away from the current approach, going from famine to feast where we give the Ukrainians a whole bunch of equipment and appropriate a lot of money, but infrequently,” Barros said, noting that the last appropriation from Congress was in December, 2022.

“We give them enough to evade catastrophe once the situation becomes very dire, but it’s not enough. As long as we have policies that deliberately tie Ukrainians’ hands behind their back, as long as we send aid in a way that’s counterable by Russian command, we’re not going to allow the Ukrainians to be successful.”