It's really a chemical kinetics problem that I would need to draw pictures for, but I'll try my best do to it with words.
High blood pressure is usually a results of your kidneys bloating and putting pressure on the capillaries and at the same time increasing your blood volume. I.e., there's more blood to push around in a smaller space so the pressure goes up.
If you're a researcher and you look at this, you'll quickly come to the conclusion that your kidneys have a lot of salt in them and this makes sense. The increased level of salt requires more water to dilute the salt so if the kidneys have lots of salt, they'll also have lots of water which will cause your blood pressure to rise. So the simple answer is "salt causes high blood pressure". And this is where everyone stops.
The next step, which we don't talk about, is WHY do your kidneys have lots of salt? Is it because you ate a lot of salt? Or is it something else? If your kidneys are getting the right signals from your other organs (e.g., your liver). They will flush the salt out with your urine. That is, it doesn't matter how much salt you eat (within reason), your kidneys can just get rid of it when you pee.
Conversely, if you're not getting the right signals, then your kidneys will hoard salt (and thus cause high blood pressure). They will hoard all of the salt they see and never (again within reason) dump it in the urine.
So to summarize:
Proper signalling: salt leaves the kidneys faster than it comes in, so excess salt is always purged.
Improper signalling: salt is hoarded in the kidneys, so even minimal salt builds up
So the question is, what's causing the screwed up signalling? Your liver being overburdened with metabolizing fructose. So fundamentally it's the fructose that's driving the high blood pressure, not the salt.
Think of it this way:
If you're getting the signal to purge the salt, then as soon as you see it in the blood, you pull it out of the blood and drop it in the urine. And as long as you can get it out of the blood faster than you can eat it, it never builds up.
If you're not getting the signal to purge (or are getting a signal to hoard), then every molecule of salt you see, you keep. So even if you eat a crazy low sodium diet, there's always a little salt around and when you see it, you keep it.