Who they want to run against, and why

The pro-Trump New York Post is pushing for Sanders.

Hillary Clinton is unraveling quickly

The GOP Is Still Hoping It’ll Have a Chance to Red-Bait Bernie Sanders

And he has provided lots of juicy material, both in years gone by and more recently, given he has all his life been chummy with and welcomed the support of people and organizations blatantly too red for prime time.

Despite Polls, Republicans See Sanders as an Easier Opponent

[P]rominent Republican operatives are chomping at the bit to face Sanders, a U.S. senator from Vermont and self-described democratic socialist, in the general election, believing he'd be an easier opponent than the former first lady, U.S. senator and secretary of state.

“Republicans are being nice to Bernie Sanders because we like the thought of running against a socialist. But if he were to win the nomination the knives would come out for Bernie pretty quick,” said Ryan Williams, a former spokesman for 2012 GOP nominee Mitt Romney's campaign. 

“There's no mystery what the attack on him would be. Bernie Sanders is literally a card carrying socialist who honeymooned in the Soviet Union. There'd be hundreds of millions of dollars in Republican ads showing hammers and sickles and Soviet Union flags in front of Bernie Sanders.”

. . . .

At a debate in January, Kasich joked that “we're going to win every state if Bernie Sanders is the nominee.” 

The same month, RNC chief strategist Sean Spicer tweeted Sanders-friendly commentary during a Democratic debate and quipped that he was trying to “help” the underdog.

“Most Americans have only a vague image of Bernie Sanders,” Jack Pitney, a political science professor at Claremont McKenna College, said in an e-mail. 

“They see him as a truth-telling outsider, which they find appealing. It’s very likely that many voters do not know that he is a self-described socialist. Although the socialist label isn’t nearly as toxic as it used to be, it is still a big negative. In a 2015 Gallup survey, 50 percent of Americans said that they would not vote for a socialist.”

Williams argued that “for decades, Republicans have tried to paint Democrats as socialists and he literally is a socialist.” 

He said Sanders, who has been powered by small-dollar donations, would have a tougher time raising the money expected of a general election candidate—in 2012, the campaigns of President Barack Obama and Romney, along with allied groups, raised more than $1 billion.

If general elections are about mobilizing one's base and winning over undecided voters, Williams argued that Sanders is less likely to win over the latter.