"I don't want to hit Crazy Bernie Sanders too hard yet because I love watching what he is doing to Crooked Hillary. His time will come!," Trump said in one of his two tweets.
"Big wins in West Virginia and Nebraska. Get ready for November - Crooked Hillary, who is looking very bad against Crazy Bernie, will lose!" the real estate tycoon said.
Trump said he has not started attacking Sanders yet.
Sanders last night won the West Virginia primary after which he claimed that he can easily defeat Trump.
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"Donald Trump is not going to become president for a number of reasons," Sanders said in his address to his supporters in Oregon.
"The major reason is that the American people understand that we cannot have a president who has insulted Latinos and Mexicans. Who has insulted Muslims? Who every day is insulting women in one way or another? Who has insulted veterans like John McCain and others?" he asked amidst applause from the audience.
And that movement was a "very ugly effort to delegitimise the presidency of the first African-American president" in our history.
Trump will not become president because the American people understand that our strength is in our diversity, Sanders said.