After pausing their multimillion-dollar advertising campaign to review their strategy, the Trump campaign plans to launch new ads on Monday depicting Joe Biden as a puppet "controlled by the radical left," according to two senior campaign officials.

Why it matters: The Trump campaign's most recent internal polls show the "puppet of the left" attack on Biden is beginning to resonate with voters, per two sources briefed on the polling. And it sets the campaign up to attack Biden's vice presidential selection.

• "The 'radical left' is a placeholder for Biden's VP pick," said one adviser.
• The new ads will get into specific policy areas, likely including taxes (see Friday's WSJ editorial: "Read Joe Biden’s Lips: New Taxes").

Behind the scenes: Trump campaign officials are frustrated that Biden's "very unfavorables" aren't as high as they'd like them. Voters don't intensely despise him the way many despised Hillary Clinton. And several Trump advisers have told me they doubt they can find a line of attack that will make Biden as hated as Clinton was in 2016.

• Instead, Team Trump is trying to persuade voters that if they vote for Biden, they're not actually electing this amiable, moderate old man. The only way they believe they can sufficiently toxify Biden is to convince voters that he's an empty vessel to be filled by the policies of the "radical left."
• That's why the Trump campaign has made so much of Biden's policy partnerships with Bernie Sanders and Alexandria Ocasio-Cortez.

Between the lines: This strategy makes Biden's VP pick especially important for Team Trump, advisers say. If Biden's running mate is hard to depict as a wild-eyed radical, this empty vessel strategy won't pack the same punch.

• But if Biden picks somebody who has higher "very unfavorables" than he does, watch for the Trump campaign to try to persuade the public that this VP bogey-woman is actually the person they are electing president.

Jason Miller, a senior Trump campaign adviser, put it this way: "Biden's VP pick is effectively his political living will, for a candidate who has already said he's merely a transition to the next Democrat and has refused to commit to serving a second term."

• The Trump campaign spent much of Saturday attacking Biden for considering Bass to be his VP.
• They're attacking Bass because they see an opportunity to tag Biden with views and associations — her public comments sympathetic to Fidel Castro — that are toxic to a substantial number of voters in Florida, a senior Trump campaign source told me.
• The Trump campaign held a press call Saturday with Florida Sen. Marco Rubio and Florida Lt. Gov. Jeanette Nuñez to amplify this line of attack.

Response from the Biden campaign: Andrew Bates, director of rapid response, said, "The American people know Joe Biden. And after seven consecutive months of failed leadership during the worst public health crisis in generations, they know that our nation's capacity to join the rest of the world in beating back COVID-19 has been crippled by one overriding burden: Donald Trump."

• "That's why the Trump campaign is locked in a sad and pathetic cycle of bimonthly, shambolic message 'resets' — all of which are based on the same recycled lies that voters have seen through countless times before."

Go deeper: Biden succeeding in making 2020 about Trump