Well, I think we now have a better understanding of the Ukrainian strategy vis a vis the Crimean Bridge. I have speculated before on why the bridge had not been hit, but the fact that the bridge was hit today gives us more insight.
By damaging the bridge, and not destroying it, Ukraine achieves a few things.
1) It still allows the bridge to be rebuilt, so that the Russians are not more committed to taking the "land bridge." During the Yom Kippur war, the Israelis attacked the Aswan Damn with red paint—the signal being clear, we can hit the bridge, so don’t make us pull the trigger. This shows a Ukrainian willingness to hit the bridge and will harm Russia’s logistical efforts, but like the bombs containing red paint, it allows future damage done to the bridge to give them leverage in possible negotiations. Much as is the case with a kidnapping, it is often better to bargain using the threat to do harm than it is to bargain after having done harm. This attack on the bridge is a little like sending an ear from the person you kidnapped to the person expected to pay the ransom.
2) It coincides with the push that will likely happen against Melitopol, which will cut off the "Donbas pathway" of supplies to the area around Kherson. Between the bridge damage and the offensive, a large number of soldiers in the Kherson region will be cut off and undersupplied. We can expect a Melitopol offensive and a renewed offensive in Kherson to follow this up in short order, before the bridge is fully operational again.
3) If Ukraine had hit the bridge earlier in an asymmetric attack, the Russians might have stepped up their "anti-terrorism" measures. Given that irregular means were the only ones they had, it made sense to wait till the moment where the strike would provide the most benefit to Ukraine’s military efforts. (We will discuss other possibilities regarding how this attack was carried out below, but asymmetric warfare seems the most likely explanation at the moment.)
4) It is also important to note that the attack occurred on the Ukrainian side of the bridge—so they are still adhering to US guidelines not to hit Russia’s actual territory. It also happened in the early hours so as to minimize civilian casualties. In no way can any sane person describe this attack as terrorism. Terrorist attacks seek to maximize casualties, not minimize them.
5) The attack coincided with the crossing of a train carrying fuel across the strait. This means that the Ukrainians had insight into what cargo these trains were carrying—and likely, unless they got quite lucky, timed the attack rather precisely to coincide with the train’s passing. This is a reason to think that Ukraine may have used a boat loaded with explosives rather than a truck—as the explosion itself suggests massive damage done to the underside of the bridge while a truck bomb would have done more damage to the roadway itself (and would have wasted a great deal of explosive power in the process)—which fell into the water largely intact. That said, a “boat bomb” would likely have focused on taking out the rail portion of the bridge as that is the more logistically important.
6) We know this was not an accident, and any suggestions it was are absurd. First, the explosion occurred as a train carrying fuel was crossing on the other side. Second, the explosion occurred at one of the bridge’s weakest points. It was not an accident.
Another possibility is that Ukraine has modified its Neptune missile to function as a cruise missile.
If you look at the footage carefully, the way some of the sparks resulting from the explosion fly do not seem consistent with an explosion that originated on the roadway itself. It is quite possible for the story regarding how this attack was carried out to change. I think a truck bomb remains the most likely explanation for now, however.
6) It confirms that Ukraine has special forces operating in not only Crimea but Russia itself as the truck was crossing from the Russian side. The Ukrainians are sending a very sinister message with this attack: We have operatives in Russia and chose not to hit you on your territory, but we could.
The timing needed to carry off the attack, esp. if they did use a truck, is quite spectacular. This was clearly carried out by some of Ukraine’s best operatives. Setting off the truck bomb without using a suicide bomber requires a fair bit of ingenuity, I imagine. That said, it is possible Ukraine found someone with terminal cancer and offered to take care of his family after his death if he agreed to carry out such an attack. (Such a man should be lauded as a hero—not truly a suicide but a man laying down his life for his country and for his family.)
No matter what was done, it is a masterpiece of operational art suggesting that the Ukrainians are starting to rival Massad in terms of sophistication.
That said, I actually think the attack was not quite as successful as had been hoped—I think they hoped the explosion would ignite the train that was passing on the other side and lead to a structural collapse of the that side of the bridge as well. This is one reason I pushed for using a barge containing hidden explosives as well as a large amount of ammonium nitrate: As anyone who has seen the Beirut explosion knows, such an attack would have proven much more effective. Sadly, the truck bomb does not seem to have done the job as train traffic has resumed and car traffic is making progress on the undamaged portion of the bridge. The Russians are likely to be more on guard against asymmetric attacks against the bridge going forward. Unless Ukraine improves its missile technology (assuming a missile was not used here) they may have missed their chance to hit the bridge again. But then again, they may have other plans in mind as well.
If Ukraine has other ways of hitting the bridge, another attack focusing on the rail portion might happen in the not too distant future.
My guess, it was a suicide bomber---likely someone with terminal cancer who, instead of a long agonizing death preferred to die for his country.