Why was pressure building for a new constitution during the second half of the 1780s?

The reason is that the country was in a lot of debt .

Explanation:

America defeated Great Britain during the 1780s, won the battle, and set up a system of government. This composed of success, confrontation, political and economic turmoil and development. The American Revolutionary War concluded in 1783, with George Washington becoming America's first president elected in 1789.

After the battle, the nation had great debt and France just lent money at immense inflation. Paper currency has little value, and coins that caused a major economic recession were hard to obtain. The accumulation of debt and failure to pay debt contributed to revolts like Shay's uprising. For contrast, the United Kingdom declined to buy US goods.

While American colonists in the 1780s had trouble, if this decade of litigation, errors, progress and independence, the nation would not be that today.

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.