WASHINGTON — President Donald Trump has been ramping up his attacks on Bernie Sanders as the Vermont senator has consistently stayed near the top of the Democratic pack.

Trump lobbed a fresh jab at Sanders on Sunday on Twitter, noting his rise in the polls, and brought him up throughout his rally on Thursday in Toledo. Trump's campaign sent out back-to-back emails blasting Sanders last week.

The moves are part of a deliberate shift in focus towards Sanders, a campaign official said. As Trump’s attacks are likely to do more to help Sanders than hurt him with Democratic voters, it's an indication the campaign is trying to put its finger on the scale in the weeks before voters begin weighing in.

“Wow! Crazy Bernie Sanders is surging in the polls, looking very good against his opponents in the Do Nothing Party,” Trump tweeted Sunday. “So what does this all mean? Stay tuned!”

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Sanders shot back moments later, replying on Twitter, "It means you’re going to lose."

Sanders took a narrow lead in the most recent poll of Iowa voters, but the race there remains essentially a four-way dead heat less than a month before the critical first-in-the-nation caucuses. The Des Moines Register/CNN/Mediacom Iowa poll, released Friday, shows Sanders with 20 percent support among likely Democratic caucus-goers.

While Trump's campaign advisers believe the president has a good shot at defeating any of the Democratic contenders, they have said Sanders would be an easy mark because they believe his progressive policies would alienate moderate and independent voters.

But the campaign has also sought recently to go after Sanders’ character, not just his policies. In a campaign email sent Thursday, Sanders was described as a "wealthy, fossil-fuel guzzling millionaire” — a somewhat paradoxical attack from a billionaire who used to fly around in a private jet. In another on Wednesday, the campaign said Sanders "can't be trusted to defend American lives."

“He’s just another Hollywood-style hypocrite who demands working class Americans make sacrifices while he plays by his own rules and enjoys a lavish lifestyle," the campaign email on Thursday said.

Although Trump often refers to Sanders as "crazy Bernie," he has previously reserved his most stinging attacks for Democrats like Biden and Warren.

But at a campaign rally in Toledo Thursday, Trump went after Sanders several times, attacking the senator's health care plan and his criticism of the administration's decision to kill top Iranian Gen. Qassem Soleimani, while seeking to paint Sanders as a leader of the Democratic Party.

“Democrats are taking their cues from socialist Bernie Sanders," along with the group of freshman women in the House known as "The Squad," Trump said. "They're the leaders of the party."

Trump's attacks haven't gone unnoticed by Sanders.

"Some of you may have noticed that recently our campaign and me personally have been the target of attacks from Trump and the Republican party because they are catching on that our campaign is the campaign that can and win defeat them,” Sanders said at a town hall event in Newton, Iowa, on Saturday. "We are going to expose the fact that when Trump talks about being a friend of working people, he is a liar and a fraud."