Delaware was a loyal slave state.
And that's the thing - the Trent affair has the serious potential to cause a catastrophic collapse of the Union military position. They can actually end up with fewer troops in absolute numbers than the Confederacy if the small arms issue is particuarly nasty, their banking system can more or less collapse, and the Union then has to allocate something like 1/4 to 1/3 their army to defend against the British (coast and Canada). That's a situation in which the Confederacy absolutely could start winning decisive victories on several fronts, and every time they carry the field they capture small arms the Union can ill afford to lose.
Summer 1862 is the point the Union started mobilizing its advantages, OTL - but it was still dependent on things like European small arms, and the army was not nearly as good as it would become in 1863.
It's a situation the Union could rectify given enough time, of course - it's still stronger industrially and has more manpower, so the problems are temporary - but in Summer 1862 under these conditions the Union is going to have to make some very hard choices about what to defend... and I think it's entirely possible that when the dust settles on the way into autumn there are Confederate boots on the ground in much of the contested territory.
So, if the Union is forced to make choices about where to defend, and will then be forced to contemplate whether to trade Occupied Maryland for Kansas - what would be their priority list?