Discuss the advantages and disadvantages of being an office incumbent in Washington, D.C. Which incumbent is more likely to win an election—a congressional or a presidential incumbent? Why?

As a matter of historical statistics, in the second half of the twentieth century and the beginning of the twenty-first century, incumbents have enjoyed re-election rates of over 80 percent when running to retain the seats they occupy in Congress. Presidents running for second terms also display a significant incumbency advantage. Members of Congress enjoy a slightly larger advantage, but this is within the margin of error caused by a small sample size for presidents.
There are several reasons for this incumbency advantage. The first is that incumbents have the advantage of free publicity and extensive free media coverage. Rather than having to fight bruising primary battles, they can focus on the election itself and are not as likely to be compelled to pander to an ultra-partisan base in primaries in a way that might have an adverse effect on their chances in a general election; although in our current era of hyper-partisanship, this may be changing.
There are a few circumstances in which incumbency can be a disadvantage. While people tend to support incumbents when they feel safe and prosperous, in times of economic downturns or social insecurity, voters can react by voting against the status quo, often for populist or other "outsider" candidates. Midterm elections during an unpopular presidency can also go against incumbents.
http://cstl-cla.semo.edu/rdrenka/ps103/Spring2010/congressional_incumbency.htm