Question

When economists determine that a nation’s GDP has declined, they can point to this as a sign of

Answer 1

When an economist determines that a nation's GDP has declined, they would most likely point this to a sign as economic decline in a nation. When a nation produces less then it used to (comparing one year to another) this would mean that their economy wasn't expanding but was in fact decreasing in size. 

Answer 2

GDP is a measure of the total output of goods and services produced by a country over a given period of time, usually one year.

This means that GDP is a measure of the country's wealth, when GDP grows, it means that the country has become richer. On the contrary, the fall in GDP means a decrease in the wealth of that nation.

Therefore, the decline in GDP is a sign that the country has become poorer than before.