Russian air defenses have already demonstrated to be utterly unable to protect Russia from relatively simple Ukrainian low speed long range drones.
If the west authorizes accurate and effective longer range tactical weapons, Russia's air bases and rear logistics once again fall within range of precise and effective western weapons and they will begin to take major aircraft losses on the ground they cannot replace quickly enough. That will substantially hamper their air launched glide bomb attacks as air support as they will have far less launch aircraft availability. That can make a substantial difference on the ground for Ukrainian ground defenses, who will then be able to hold forward positions with fewer losses.
That in turn makes Russian wave assaults most costly for Russia as they take higher proportional losses. It can have a as significant effect in the basic calculation of the war: the strategic implications of higher losses are no longer worth future gains, so Russia may decide to negotiate a settlement. It's pretty simple, and probably what Trump was going to do anyways: carrot anc stick. Apply much higher pressure to Putin but give him an incentive also to bring things to an end by pressuring Ukraine to ceding Putin enough gor him to save face.
There really is no other course in this except the alternative of abandoning Ukraine to major defeat over time, which in turn strategically harms the USA as we are seen to be weaker and a less credible threat and a less worthy partner or ally. That perception has economic and geopolitical consequences that are very real. Maybe you accept those consequences, but one of them is that it does encourage emerging rivals and additional foreign aggression contrary to our interests elsewhere.
We broke it, we bought it. We'll have to make the best outcome for us of it, and being on the side that takes a devastating loss is generally not good.
