Although the US have been incredibly supportive to Ukraine in facing off its old foe, as you allude to this is an issue in Europe and so the EU and the UK should be firmly committed to ensuring victory for Ukraine to ensure stability. Canada and Japan have been very supportive also and I suspect that once the situation in Gaza settles that Israel will become active. Putins gamble there will backfire.
I agree that they should, but then again the US also should. We now live in an era where Kenneth Waltz's uniform billiard-ball, interest-based model of predicting state behavior in international relations no longer works well, and Bob Putnam's two-level games concept is in ascendance. That latter concept has been expanded and extended by any number of people, but it's still often the cleanest way to think about a problem due to its simplicity.
As an example, Europe's ability to respond to the situation would be diminished if it were Corbyn, rather than Starmer, who was on the threshold of power. Corbyn would have tools like the whip and cabinet ministries to hand out as a means of quelling internal party dissent over his preferred Ukraine policy. The result would probably be conflict internal to Labour, and a delayed, watered-down response by the UK.
If Corbyn had been in power for a bit, his toolkit for pushing back against internal dissent would be diminished. He would no longer have the cabinet ministries to hand out, so I would expect a stronger and swifter response from the UK, but not as strong as the one Starmer would produce. Strangely, his hand is strongest at the moment right before he wins the election, diminishes sharply the day after the Cabinet ministries are settled, and then increases again as his ability to conduct a Cabinet reshuffle without looking like an idiot increases.