It’s been a great summer for President Barack Obama.

Late last month, his chief domestic policy accomplishment, the Affordable Care Act, was upheld for a second time by the Supreme Court.

One day later, the same court then enshrined the right to marry for same-sex couples, a move his administration supported.

Then, this week, he secured a historic deal to keep Iran from building a nuclear weapon, which if successful, would be a major foreign-policy victory.

But six and a half years after Obama took office, one of the first items he vowed to check off as president remains undone: closing the Guantanamo Bay prison. ...

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