Why does too much dietary intake of sodium possibly lead to a stroke or TIA? Is it that the blood level gets too high or the blood pressure?

Dietary sodium. This is a sophisticated question. The answer is complicated. Dietary sodium (salt) tends to increase the circulating blood volume; some people are more sensitive than others. Kidney neurohormonal factors regulating the blood pressure are affected. In the end it is high blood pressure which over many years can damage arteries and lead to increased risk of heart attack and stroke.