Online advertising can be used to mislead, deceive, and manipulate Internet users, and political advertising is no exception. In this paper, we present a measurement study of online advertising around the 2020 United States elections, with a focus on identifying dark patterns and other potentially problematic content in political advertising. We scraped ad content on 745 news and media websites from six geographic locations in the U.S. from September 2020 to January 2021, collecting 1.4 million ads. We perform a systematic qualitative analysis of political content in these ads, as well as a quantitative analysis of the distribution of political ads on different types of websites. Our findings reveal the widespread use of problematic tactics in political ads, such as bait-and-switch ads formatted as opinion polls to entice users to click, the use of political controversy by content farms for clickbait, and the more frequent occurrence of political ads on highly partisan news websites. We make policy recommendations for online political advertising, including greater scrutiny of non-official political ads and comprehensive standards across advertising platforms.