The average retail price of diesel in the United States topped $6.50 per gallon this weekend amid a worsening global fuel crunch that threatens to hit economies, including the world’s largest. The national average diesel price jumped to $6.5050 per gallon as of Sunday, according to data from AAA. The price hike to $6.50 from the $6 mark reached only two weeks ago was very steep, as the international Brent oil benchmark remains at $100 per barrel and fuel supply from the Middle East and Russia remains heavily constrained. A month ago, the…