President Obama toured Old Havana in the rain, Sunday, March 20, 2016 in Havana, Cuba. (AP Photo/Pablo Martinez Monsivais)

President Obama arrived in Cuba yesterday, making him the first sitting American president to visit the nation since Calvin Coolidge did so 88 years ago. Coolidge went there in 1928, in his first trip abroad as commander-in-chief, to speak at the Pan-American Conference.

Today, the president's island visit is symbolic of a new era of diplomacy between the two countries—the trip comes roughly a year and a half after the United States formally reestablished diplomatic relations with Cuba. It's also a way for Obama to highlight the progress he still hopes to see in his remaining time as president, namely for the U.S. Congress to lift the trade embargo.

WHAT WE'RE WATCHING THIS WEEK:

* This week's episode of the Presidential podcast is now live. We're up to James K. Polk, and with him we explore the difference between being remembered as an effective president vs. a great president.

* Twitter turns 10-years old today.

* Apple and the Justice Department are back in court on Tuesday over the iPhone encryption case.

* Arizona is among the six states that will hold presidential primaries or caucuses this week.

* On Wednesday, after wrapping up his Cuba trip, President Obama will head south to Argentina.