Let's start as Marxists telling it like it is.  Donald  Trump is not simply a "hate monger."  People hate various things, both personal and polititical.   Trump is a racist and a fascist, and the two go hand in hand.

"Muslims" are for Trump what "Jews" were for Hitler, a "problem", a "subversive force," an "enemy within." 

Throughout Europe and North America, as anyone with an understanding of history can see, Anti-Muslim bigotry is becoming for the right  the  New" Anti-Semitism." 

Parties that Europeans  have tradionally considered fascist, like the National Front in France, have soft-pedaled their traditional anti-Semitism, including Holocaust denial for anti-Muslim bigotry, 

Some have even come to support Israel s a defender of "Western civilization" in the Middle East" from the barbaric  "Muslim" hordes, much as Hitler proclaimed his Japanese allies "honorary Aryans" because they  represented  the worship of military power and leaders  that characterized the "superior races" defending civilization from the barbaric hordes(in reality because they were his allies, as the Israelis are  the allies of the U.S./NAT0 bloc in the Middle East 

Trump builds upon conventional racist  and xenophobic views, which frankly have also played a significant role in U.S. history locked in conflict with anti-racist, egallitarian, cultural pluralist views,

 But takes them a step further, like Hitler and his many imitators through the world in the period between the two world wars.

Now, Trump has called for a "ban" on all Muslims entering the U.S., something  resembling the "oriental exclusioon" policies of the U.S. government  from the 1890s on.  And to compound the demagoguery, Trump has thrown in the internment of over 120,000 japanese during WWII,  a policy repudiated in the courts in 1983 and by Congress in 1983, with an apology and limited reparations to survivors---that no one  for many decades has openly defended on any level  for decades.  Of course, Trump has  dodged the question of whether he would have "voted" to intern the  Japanese at the time, saying only that war is tough and that America today is soft and no longer wins wars

So Hitler's "Asiatic Hordes" led by  Judeo-Bolshevisim" marching from the Russian Steppes to conquer and destroy European civiliztion becomes for Trump, Muslim infiltrators come to use murder Americans as part of their global holy war.

Does it pay to  tell Trump that WWII was won against the Axis alliance, whose core ideology he imitates?  Probably not?

  Does it pay to tell Trump that the court decision overtuning an earlier Supreme Court decision(1944) upholding the internment stated clearly that lawyers defending the decision before the court with-held from the judges  the facts tht the government new that the Japanese constituted no real security threat?  Probably not.

  Does it pay to tell Trump that WWII that the Allies included the U.S., Britain, the USSR, and millions of  partisan fighters in Yugoslavia, Greece, the Soviet Union, China, IndoChina, the Phillippines, and that the Soviet Union made the largest contribution to victory by engaging  nearly 90 percent of all European Axis forces between 1941 and 1944?  Probably not.

Would it even pay to inform him that those who win wars are really the ones who suffer the least casualties and end up in the best position in terms of economic power.  The U.S. was in that position after the two world wars, but the cold war of course was very different.  The U.S. paid the most for the NAT0 alliance and then of the major, discounting China in both its revolutionary civil war and the Korean War(before it really took off with the development of its Socialist Market Economy) suffered the most dead and wounded

The Marxist-Leninist definition of fascism, still the best,  is that fascism is the open terroristic dictatorship of the most reactionary sectors of the capitalist class in the service of finance capital. In the U.S. today, that would mean at the elite level the powerful oil, coal and natural gas corporate leaders, the military contractors, the investors in the prision industrial complex. At the mass level it would mean most white men and women frustrated by their failures to advance in society in terms of status and money, ready to blame their situation on minorities and the poor given special benefits by government, and by foreign powers stepping on a weak United States.

Fascists are successful when they enter the political mainstream and their enemies on the left are either divided or marginalized.  Fascists create  whether they come to power or not a poisoned political climate.

If history is any judge, conservatives can not fight fascists since their lives are spent fighting the moderate and militant left.  Those centrists who today are counterpoising Trump on the right with Bernie Sanders on the Left , like their predecessors who did the same thing with Hitler and Stalin before WWII under the totalitarian concept,  won't fight fascists like Trump because their real aim is to protect the status quo from militants like Sanders(if and when a leader like Sanders becomes president, they will then fight)

And those who laugh at politicians like Trump or smugly believe that he will simply divide the right and lead the Republicans to defeat  can't really fight the fascism that Trump  is peddling today.

Both Republican and Democratic politicians are issuing statements criticizing Trump's statements in varying degrees as representing  either "hate"(Clinton) or  a distortion of "conservativism" and "true American values"(some of the Republicans).  Bernie Sanders has answered Trump directly and clearly in the following with the following words

“Demagogues throughout our history have attempted to divide us based on race, gender, sexual orientation or country of origin. Now, Trump and others want us to hate all Muslims. The United States is a great nation when we stand together. We are a weak nation when we allow racism and xenophobia to divide us.”
Read more at http://www.inquisitr.com/2618075/donald-trumps-anti-muslim-rhetoric-slammed-by-bernie-sanders/#OlfFmt5mDbR5T8KL.99

Unity with content, not merely a phantom "unity" to defeat "the ultraright" by supporting lesser of two evils candidtes without  purpose or a plan is  the only way to prevent fascists from coming to power political.  The French Popular Front and the U.S. New Deal coalition, in which Communists played a major role, kept fascists from coming to power with concrete programs that improved the conditions of life for working people and gave them hope for the future and making it clear to those in the capitalist ruling classes who were ready to fund fascist demagogues and use them against the working class that the risks of doing that were too great.

  Right now, the Sanders campaign offers the best hope for fighting what Donald Trump is peddling in U.S. Politics.  Our commercial capitalist media understands that which is why they have given Trump such an abundance of publicity.  Time Magazine, true to the mindset of its founder, Henry Luce, who preached the doctrine of an "American Century" during WWII, understands that, since they apparently have made Trump one of their 8 finalists for 2015 "person of the year" and snubble Bernie Sanders.

We on the left should  realize that and work for the Sanders campaign as we supported united front struggles against Hitler and his many imitators in the past.  That is really the best answer that we can give to Trump and the "little Trumps" who are running against him in the Republican primaries