Even as Mitt Romney inches steadily towards securing the Republican presidential nomination, his standing in the eyes of American voters continues to slip.

A new Washington Post/ABC News Poll found that fully half of Americans said they have an unfavorable impression of Romney, a former Massachusetts governor, compared to 34 percent of voters who said they viewed Romney favorably.

That is the highest unfavorability rating for Romney yet recorded in a Washington Post/ABC poll, and seems to confirm that perceptions of Romney are deteriorating as the nominating contest drags on -- a Washington Post/ABC poll conducted in February found that voters said by a 2-to-1 margin that they liked Romney less the more they learned about him.

While Romney has opened a substantial lead in pledged delegates for the Republican national convention, exit polls have indicated that voters choose Romney out of pragmatism more than idealism. Romney consistently captures a majority of voters who say defeating President Obama is their priority, whereas voters who say they most value a candidate who is a true conservative or has strong moral character have tended to choose Romney's Republican rivals.

Polls generally predict a tight race in a hypothetical general election matchup between Obama and Romney. But the latest Washington Post/ABC news poll underscores a wide favorability gap between the two men: more voters viewed Obama favorably than unfavorably, by a 53-43 margin.