| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 28,306 | 12,370 | 41,353 | |
| 2020 | D | 30,948 | 12,755 | 44,582 | |
| 2016 | D | 28,497 | 12,795 | 43,261 | |
| 2012 | D | 32,501 | 12,858 | 45,922 | |
| 2008 | D | 32,327 | 13,984 | 46,665 | |
| 2004 | D | 24,112 | 15,212 | 39,534 | |
| 2000 | D | 22,286 | 12,628 | 35,455 | |
| 1996 | D | 22,150 | 10,686 | 35,409 | |
| 1992 | D | 20,416 | 12,575 | 37,599 | |
| 1988 | D | 19,698 | 16,087 | 36,059 | |
| 1984 | D | 21,623 | 18,940 | 40,801 | |
| 1980 | D | 20,900 | 13,660 | 35,949 | |
| 1976 | D | 22,837 | 12,872 | 36,246 | |
| 1972 | R | 13,124 | 20,090 | 34,350 | |
| 1968 | D | 15,734 | 9,402 | 37,381 | |
| 1964 | D | 16,073 | 8,420 | 24,544 | |
| 1960 | D | 15,003 | 10,669 | 25,916 | |
| 1956 | D | 5,683 | 5,390 | 11,436 | |
| 1952 | D | 6,188 | 3,621 | 9,855 | |
| 1948 | D | 4,612 | 2,056 | 7,381 | |
| 1944 | D | 5,735 | 1,129 | 6,877 | |
| 1940 | D | 5,053 | 675 | 5,753 | |
| 1936 | D | 5,617 | 861 | 6,509 | |
| 1932 | D | 3,344 | 1,840 | 5,294 | |
| 1928 | R | 2,587 | 3,474 | 6,061 | |
| 1924 | D | 2,206 | 604 | 3,413 | |
| 1920 | D | 3,228 | 1,061 | 4,348 | |
| 1916 | D | 1,368 | 376 | 1,811 | |
| 1912 | D | 1,529 | 64 | 1,935 | |
| 1908 | D | 1,154 | 407 | 1,570 | |
| 1904 | D | 1,151 | 247 | 1,427 | |
| 1900 | D | 1,743 | 566 | 2,332 | |
| 1896 | D | 1,380 | 769 | 2,204 | |
| 1892 | D | 1,728 | 1,052 | 2,812 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Portsmouth's electorate, shaped by a majority-Black population and a significant military and shipyard workforce, has delivered double-digit Democratic margins in every recent presidential cycle, with the 2024 gap widening past 38 points.
The Democratic margin in Portsmouth city peaked at seventy-six points in 1940. By 1976 the county had flipped, voting Republican for the first time in many years. The 2024 margin was thirty-nine points, the most Democratic-leaning result in the county's modern history.
The economic context is the key. Portsmouth city's median household income of $60,491 sits well below state and national norms, and 17% of residents live below the federal poverty line. The shift here is part of a broader realignment of working-class places across the country. The county's voting pattern over the last decade is most similar to that of Norfolk city and Sharkey County.