Using a Census estimate for electoral votes among the states:
Blank map for your use:
1. Barack Obama to William Howard Taft 1912
-- absolutely unimaginable. The Democrats have nobody like Teddy Roosevelt (unless Obama takes the role!)
2. Barack Obama -- to Carter 1980 [49 EV] or Hoover 1932 [59 EV] (roughly 10% of the possible electoral votes and about 40% of the popular votes) as the result of a bad economy or a nasty international scene for which he is given fault.
55 electoral votes -- you get to choose between Obama winning New York or a combination of Illinois and Maryland.
3. to George H.W. Bush, 1992 [168 EV]. President Obama seems to have accomplished everything that he could, but has no clue of what to do next against a dynamic challenger. There might be a weak economy.
169 electoral votes. Red -- move from optional in a Hoover/Carter scenario to sure things. Note the split of Maine. Pink -- additions. Michigan goes to Obama before Washington, Oregon, Minnesota, or Wisconsin because of the large percentage of African-Americans for a Northern state. (You could have New Jersey and Delaware as an alternative to Michigan).
4. to Gerald Ford. Bare loss [240 EV].
Old, sure states for Obama in the earlier scenario go deep red, optional go to medium red, new sure states go pink. The map looks familiar -- the choice is between all of the states that the Democrats haven't lost in a Presidential election since 1988 (243 -- include Pennsylvania), or those that have voted no more than once for a Republican nominee since 1968 except Pennsylvania (238). Choose between Pennsylvania and a combination of Iowa, New Hampshire, and New Mexico for the closest match.
5. To George W. Bush, 2004 [280 EV] After a troubled first term in which he gets away with a lot, President Obama barely wins a close election. He gets all the states in any shade of red, yellow, or white and either:
A. Virginia and Colorado (yellow) -- 280 EV
B. Ohio and Nevada (orange) -- 283 EV
C. Florida (green) -- 286 EV
(Ohio and Colorado, and Virginia and Nevada work well, too)
There may have been electoral shenanigans going on, or at least there are many rumors of such in the paranoia of the time.
Wilson 1916 is similar (277 EV with 9 fewer electoral votes to divide).
Truman 1948 [303 EV] could be approximated with the addition of Ohio to Florida (304), Virginia and Nevada to Florida (305), or Virginia and Colorado to Florida (302) -- among others. No new map is really needed for this scenario.
McKinley 1900 [292 EV] would have roughly the same map as for Truman 1948, except that in 1900 there was neither Oklahoma, New Mexico, Arizona, Alaska, nor Hawaii, and DC wasn't voting. That is 18 fewer electoral votes, and it might as well be considered "antiquity" as voting goes. I have said little about McKinley and Wilson, which is just as well.
So far that is one more than half (10 of 18) of all re-election bids since 1900. Others are landslides.
Remaining -- T. Roosevelt, 1994; Coolidge 1924; FDR three times, Eisenhower, LBJ, Nixon, Reagan, and Clinton. Clinton is next-closest, and his re-election bid has a big gap between his and the next-largest (surprisingly, Harry Truman).