I'd put forth Lyndon Johnson, 38th President of the United States.
His primary objectives coming into office were progress in Civil Rights, and the eradication of poverty in the USA.
He did actually manage to get the Civil Rights Act passed, and did some good work on poverty. However, he then got sidetracked by the escalating fiasco in Vietnam, so his poverty program never really got off the ground. Even most Civil Rights leaders ended up railing against him over the war. It became so unpopular, he didn't even bother running for a second term.
Today he's cheifly known for the Vietnam war. His anti-poverty campaign is almost completely fogotten. Even those who give him a little credit for the Civil Rights Act generally proceed to mention how passage of it nearly destroyed his party. Before Johnson, the South used to vote solidly for Democrats. After the Civil Rights Act, the entire South deserted the Democrats, and Republicans held the White House for 20 of the next 24 years.
If we just look at his poverty goals, he perhaps was successful during his tenure. However, the fact that later presidents didn't share his goals had effects that can be easily seen on a simple graph.
(You could make various cases for various blips, but the overall trend is clearly a turn-around of the previous downward trend into an upward trend)