The US could be heading for two good years — at least if you are a Republican supporter. Not only will the party's presidential candidate Donald Trump be moving into the White House on January 20 — the right-lurching GOP (Grand Old Party) has also won control of the 100-seat Senate and retained control of the lower chamber, the US House of Representatives.

Since the 1858 midterm elections, the first to pit Democrats against Republicans in a two-way race, voters have delivered a so-called "unified government" a total of 48 times. Democrats have enjoyed the upper hand 23 times, Republicans 25. The parties have split control of the White House and at least one chamber of Congress a total of 38 times during that same period.

Usually, the president's party does not retain its grip on a Congressional majority for long. "Although a single party in charge in Washington is common at the beginning of a new president's term, there has only been one presidency since 1969 where control has lasted beyond the following midterm election," writes Katherine Schaeffer of the Pew Research Institute.

Midterm Congressional elections are held at the halfway point in the president's four-year term. Democrat Jimmy Carter was in fact the only president ever to secure and maintain control of Congress for the entirety of his four-year term (1977-1981). Still, he was voted out of office in 1980, making him a one-term president.

Presidents are keenly aware of the fact that their hold on a Congressional majority is potentially fleeting, says Nolan........

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