Washington: Americans' views of presumptive Republican nominee Donald Trump have drifted slightly more negative over the past month and a half, while his Democratic rival Hillary Clinton's image remains steady, according to a Gallup poll. Trump's net favourable rating slipped to -33 for mid-June, from -28 in the first week of May, according to the poll released on Tuesday. At the same time, Americans' view of Clinton has remained significantly less negative and more stable, with a current -13 net favourable rating, Xinhua cited the Gallup as saying. By this point in an election cycle, when each party's nomination has been clinched, candidates typically have had a more positive image than has been the case for Clinton and Trump. Since 1992, Gallup has tracked a few presidential candidates with a negative net rating in June and July of an election year, Gallup found. The last month and a half has been an eventful period for both candidates. Trump for instance secured the number of delegates he needed to win the nomination. He also attracted a great deal of attention by questioning the impartiality of the federal judge who is hearing a case in which he was being sued by a former student of Trump University who claimed he did not get his money's worth. Both candidates also made highly publicised comments following the tragic shootings earlier this month in Florida, which underscored how each might handle such an event as commander-in-chief. Americans' views of Clinton improved modestly after she secured her party's nomination early the month, but that basically represented a return to where her image had been in early May -- better than Trump's but still negative. On the other hand, Americans' views of Trump began to worsen in the final weeks of May and have continued to slip since. Importantly, the trend reflects a slow slide, rather than an abrupt change in response to any specific event of the past month and a half. Gallup has been tracking the US public's views of Clinton and Trump since mid-July 2015. Since then, both candidates' images have become more negative. Americans' views of Clinton have consistently been more positive compared to Trump, with the exception of a brief period last August.