After the negotiations for the Transatlantic Trade and Investment Partnership (TTIP) triggered massive public mobilization in the European Union (EU), literature emerged on the novel 'politicization' of trade in Europe. To be sure, public salience was high around the TTIP negotiations. However, public salience over EU trade and investment negotiations has varied considerably over the past two decades. The objective of this paper is to stimulate a research agenda explaining such variation. After presenting evidence of variation (over time, across contemporaneous negotiations, and across Member States), we review a diverse set of literature to lay out six complementary explanations for why some trade deals provoke public salience, while others do not: changing nature of trade and investment negotiations; growing discontent with globalization; transformation of the media landscape; institutional changes brought about by the 2009 Lisbon Treaty; the role of the United States; and foreign interference.