Only 25 percent of voters think Trump is a serious candidate for president, which has literally not changed since 1999. At that time, 23 percent of voters viewed Trump as a serious candidate when he ran briefly for the Reform Party’s nomination the following year. Right now, 74 percent thinks he’s not serious, and that figure hasn’t changed since 1999 as well. One third of the country views him favorably, which is abysmal. But more Republicans tend to view him as a serious candidates when you break it down by party–and they also view him in a much more favorable light as well (via Gallup):
While a consistent percentage of Americans take Trump's presidential candidacy seriously, views by party groups have changed over time. Today, with Trump competing for the GOP nomination rather than a third-party bid, 41% of Republicans say they consider Trump a serious candidate, compared with 20% in 1999. Democrats, meanwhile, take Trump even less seriously as a candidate today (12%) than they did in 1999 (20%), while independents' views haven't changed.[…]
In general, Trump typically has been seen more unfavorably than favorably since Gallup first asked about him in 1999, with the sole exception occurring in 2005, when 50% of the country viewed him favorably and 38% viewed him unfavorably. At the time, Trump starred in the hit show "The Apprentice" and was not actively involved in the political arena.
Trump fares better with Republicans overall, with a 49% favorable rating and 38% unfavorable score. But his high-profile candidacy appears not to have won him any additional admiration among Republicans -- his favorable rating among this group is about where it was in 2005.
At the same time, a lot of Republicans can’t stand Trump, though he has tapped into a frustration over illegal immigration and the lack of the enforcement of the rule of law in general. That alone is frustrating for any voter, and Trump was the first candidate to address the issue in an aggressive manner. Moreover, his comments on trade surely will catch fire with an electorate that has become much more populist and skeptical of free trade deals, especially ones–like the Trans-Pacific Partnership– that are trying to be finalized by this administration. The boost in polls is mainly grounded in the fact that he has name recognition. Illegal immigration was already going to be an issue next year over Obama’s executive actions in the arena, and someone else (who’s more serious) is going to discuss it on the campaign trial. The death of Katie Steinle, who was killed by an illegal immigrant in San Francisco, has started a debate–or at least it should–about sanctuary cities, which purposefully skirt immigration enforcement laws. Leah found all of them, which you can read here. This only helps Trump at this point, though I hope more serious candidates (Walker, Rubio, etc.) start to channel this issue as well, and relegate the Trump candidacy to just pure entertainment because that’s what it is at heart.