After 6 months of fighting, what's next in the war in Ukraine?

When Russia invaded Ukraine on Feb. 24, the conventional wisdom among many U.S. national security officials and analysts was that Ukraine's military would be able to resist only for a few days, possibly a week.

But six months later, Russia's invasion of Ukraine has stalled as Russia's military capabilities have fallen far short of what they seemed on paper, and Ukraine's military, buttressed by a constant supply of weapons from the U.S. and the rest of the international community, has demonstrated it will fight hard in every part of the country.

ABC News asked national security analysts and a senior British military officer to discuss how the battle in Ukraine has evolved over the last six months and what could come next.

What should we expect? Can Russia succeed in a war of attrition?

In February, when Russian troops invaded Ukraine simultaneously along multiple fronts, it appeared to be an effort to overwhelm Ukraine's military in quick order.

But six weeks later the combined effects of Russia's poor military decisions and planning led to the tactical withdrawal of its forces stalled north of the capital Kyiv and a shift towards the Donbass region in the east.

Since then, months of intensive artillery barrages and rising casualties have resulted in only small territorial gains for Russian troops and as Ukraine has prepared for a counteroffensive in southern Ukraine, the fight has already begun to shift to that region.

And it has been a costly one for both Russia and Ukraine. The U.S. believes Russia has suffered between 70,000 and 80,000 killed and wounded among its military forces and in June Ukrainian president Volodymyr Zelensky acknowledged between 60 to 100 military fatalities a day among his forces.

Might there be a stalemate?

"I am guessing that some kind of a stalemate will develop in the course of the next few weeks or certainly by the cold weather," Michael O'Hanlon with the Brookings Institution, told ABC News. "And then the question will be do the two sides decide it's time for diplomacy and maybe have some creative notions of shared sovereignty or putting off certain territorial issues for a longer term referendum?"

O'Hanlon speculates there could be a lull in the fighting in Ukraine this winter as both sides rebuild their forces for a fight next year, much as was seen during World War I.

Retired U.S. Army Lt. Gen. Ben Hodges, an adviser with Human Rights First, told ABC News that Russia has moved into a war of attrition that it may not win. As the top Army officer in Europe, Hodges developed the U.S. military training program for Ukraine's security forces following Russia's 2014 invasion of Crimea.

"If you're going to do attrition, you have to have three things: You have to have a lot of people, you have to have a lot of resources, and you have to have a lot of time. And the Russians don't have any of those three," said Hodges. "So, they've chosen, unfortunately for them, the wrong strategy to defeat Ukraine."

Hodges believes Russia's logistical supply network has been stretched to its limits and will be unable to continue to resource Russian troops over the long term and he is not convinced that the Russian people will continue to support the invasion as time goes by.

"There are a lot of things working against Russia in terms of time, and so this is why I believe that Ukraine is going to win, that they're going to they're going to be able to push Russia back at least to the 23 February line by the end of this year," Hodges predicted.

Air Vice Marshal Mick Smeath, the defense attaché at the United Kingdom's embassy in Washington, is more circumspect about what lies ahead.

"I think Putin is probably shocked" at the Russian military's performance on the battlefields of Ukraine, said Smeath, who releases a daily intelligence update consisting of unclassified details from the U.K.'s Ministry of Defence Defence Intelligence.

"I'm not in his mind, but I'm sure he is looking at even now his narrow objectives, because his military campaign is failing," said Smeath. "And he is getting to a point where his troops are stagnating and he is making very, very insignificant gains whereas the Ukrainians are defending strong."

Smeath is confident that one thing that will continue for the foreseeable future is the flow of western military aid to Ukraine.

"All I can say is that as in the UK, I can certainly say the same for our American friends and all of our our partner nations, we will keep supporting Ukraine to ensure that Russia does not get any any further gains and Ukrainian protects her people," said Smeath.

Why has Russia's military not been as dominant as predicted?

Russia's military was expected to quickly overwhelm Ukraine in short order given their vast inventory of weapons, a recent modernization effort, and a switch towards a more professional force instead of just relying on conscripts. But the last six months of war in Ukraine have exposed Russia's military capabilities and left them in a far weakened state as its battalion tactical groups consistently suffered heavy casualties

"I think I'm certainly in the crowd of people that overestimated Russian capabilities and also somewhat surprised at how poorly they have performed," said Hodges who attributes some of Russia's poor performance to corruption within Russia's military "in the form of false reporting about numbers, shoddy equipment, zero quality control over things over how ammunition is stored, all the stuff, which are ways where you can make money if you're in in the system."

Russia's recent military modernization effort focused on the integration of its warfighting capability in land, sea, and cyberspace.

"In reality, that is not the case, they have not been able to do that," according to Smeath. "They've been pretty incompetent and quite ineffective."

How has Ukraine been able to hold off Russia?

"The Russians made some big mistakes" that O'Hanlon said outweighed their numerical advantage in the number of troops and technology.

To that point, O'Hanlon highlighted Russian plans to drive heavy military vehicles over fields that were not as frozen as expected that led to bottlenecks on roads that exposed them to attacks by Ukrainian fighters.

While Russia's poor performance on the battlefield may have been unexpected, O'Hanlon pointed out that there were indicators given that were indications it could happen given that "we haven't seen the Russians fight well on a large scale in a very long time."

And that includes fighting against a determined military force and population.

"I never doubted that Ukrainians would fight very well," said Hodges. "We have been working with them since 2015. So I was sure that the soldiers would do well." But Hodges acknowledges not anticipating "the resilience of the Ukrainian population. "I didn't anticipate how strong they would be in how they would deal with this," he said.

"I think Russia completely underestimated the fact that they are a sovereign nation and they were not going to be invaded by a nation that they do not want to be part of," said AVM Smeath. "I think Russia completely got that wrong."

"Russia has been I think pretty desperate and pretty ineffective with their campaign," said Smeath. "They haven't achieved anywhere near what they wanted to achieve. "

And that is also due in large measure to the constant flow of weapons and ammunition to Ukraine being provided by the United States and other countries. Early in the war American Javelin and British NLAW anti-tank missiles had an immediate impact against Russian tanks as did subsequent aid packages of Stinger portable anti-aircraft missiles.

O'Hanlon acknowledges that the emergence of American-made HIMARS rockets systems used by Ukraine to strike at Russian headquarters and ammunition dumps as much as 50 miles away has had a significant impact on the fight in the Donbass but he is not sold on the idea that they are a complete game changer.

"I think we should watch very carefully what's going to happen in these next few weeks because my guess is that we'll already start to see some limitations of what the new technologies are able to achieve for Ukraine and yes, some kind of stalemate, perhaps on better terms than exists today," said O'Hanlon.

And Hodges believes that even more sophisticated weapons will be needed if the goal is for Ukraine to defeat Russia.

"I think if if we were serious about Ukraine winning, not just avoiding defeat, but winning then we would be pushing a significant amount of weapons, long range fires, they can accomplish what we're seeing now in bits and pieces," said Hodges. "That's what would become decisive. That's what would help set the conditions for Ukraine to launch a successful counter attack