Biden’s alliance with the left has worked, but will it last?

Joe Biden wasn’t progressives’ first choice for the White House in 2020. And he wasn’t their second or third, either.

But defying expectations, liberal Democrats have emerged as the president’s most loyal allies in Congress during his first two years in office, helping to pass a massive COVID-19 relief package, a historic investment in American infrastructure and billions of dollars to combat climate change.

Their alliance was as fruitful as it was unlikely. And it could soon be put to the test.

Democrats are bracing for losses in Tuesday’s elections...