The short answer is liberalism kills. Whenever liberal/progressive policy is enacted the death toll always goes up.
In addition modern Liberalism is permeated and defined by nothing more than and little less than Communists, Socialists and Dictators. Trump's election has clearly exposed that truth for all who have eyes to see. This truth can be ascertained by simply listening to anything Chuck Schumer or Elizabeth Warren have to say; but more than listen to what they say watch how they say it.
For one more reason at its most basic level liberalism is anti-God. Or perhaps it would be more accurate to state liberalism is anti-Christian, for liberals do worship a god, the god known of as The State. Think about it, why do you believe on election night last year millions of people were actually broken down in tears, crying and wailing over the fact Clinton had lost the election? Why one year later were these same people out screaming at the sky? The answer isn't as simple as their side losing the Presidential election, the answer is their god had been cast down. This truth also accounts for the immediate and continual effort by the American left to overturn the results of the legal and constitutional election of Donald Trump, because one liberals care nothing of the Constitution or the legalities enforced therein and two they are hellbent to avenge their god. A legal election, the Constitution, Democracy, all of that can be damned.
Then you have the absolute moral decrepitude inherent in liberalism and defined by the Democrat Party throughout history. Remember, if every accusation leveled against Roy Moore is true, the actions those accusations represent all occurred when Moore was a proud Democrat, a proud member of the Democrat party.
For these and at least fifty other reasons I could give, Trump is correct, we don't need another liberal in the Senate.