He ripped Ohio Sen. Rob Portman in Columbus last week as a too-little-too-late political opportunist for disavowing Trump only after the presidential nominee boasted about sexual assault. He lashed Florida Sen. Marco Rubio in Miami as a weak-minded hypocrite who once ran against Trump but now worries about alienating his backers.
And on Sunday in Las Vegas, he declared GOP Rep. Joe Heck, running to replace retiring Senate Minority Leader Harry Reid, a closet Trump supporter, even as he's disavowed the candidate.
"How does that work?" Obama said with disdain during a raucous campaign rally here. "You're for him, but you're not for him. You're kind of for him. What the heck?"
"That's not leadership. That's cynical," Obama said. "That means you'll say anything and so anything just to get elected."
During his half-hour stump speech, Obama lambasted Trump for carrying out a "bromance" with Russian President Vladimir Putin and for suggesting the upcoming vote is rigged in favor of Democratic nominee Hillary Clinton.
"That means he's losing," Obama said on Trump's claims about the validity of the election. "It means you don't have what it takes to do this job."
Polls in Nevada show a close race, though Clinton has emerged with a narrow edge in the last several weeks. A Monmouth University survey released just before last week's debate showed the Democratic nominee at 47% support among likely voters, compared to 40% for Trump. That was a reversal from a month ago, when Trump stood at 44% and Clinton at 42%.
The state's Senate race, held to replace Reid, appears tighter. Heck stands at 45% in the Monmouth survey of likely voters, while his Democratic rival Catherine Cortez Masto, a former attorney general, is at 42%.
In his remarks Sunday, Obama reserved his harshest criticism for the GOP Senate candidate, who initially backed Trump enthusiastically but withdrew his support following tape of Trump making the sexually aggressive remarks. Obama said that kind of political reversal doesn't stand scrutiny.
"Now, when suddenly it's not working, and people are saying this guy's kind of out of line, all of a sudden these Republican politicians who were OK with this up to a point, are saying this was too much, suddenly that's a deal-breaker," Obama said. "Well what took you so long?"
"What the heck took you so long?" Obama said again with emphasis -- one of several times he deployed the candidate's surname as an attack.
And he went after a new Republican tactic, suggesting GOP lawmakers should be elected to act as a check to Clinton's power should she win. An ad in New Hampshire this week backing incumbent Republican Sen. Kelly Ayotte utilized the argument, but Obama said the senators' records should stand for themselves.
"They've been in charge of Congress now for the last six years basically, and what have they gotten done?" he said to chants of "nothing."
Obama has increasingly turned his ire on Republican lawmakers in the waning days of the 2016 campaign, casting those who have criticized Trump's behavior but maintained their endorsements as craven hypocrites. With Clinton leading in most national polls, and up in enough battleground states to signal a likely victory, the President now hopes to turn key legislative chambers, where the agenda items he's pressed for as commander-in-chief could either be cemented or eroded in the years after he leaves office.
The strategy is not without risk. In the post-election lame duck session, many of the same Republicans Obama is hammering will prove essential in approving the President's last remaining legislative priority: passage of the Trans Pacific Partnership trade pact.
Even TPP's fate in the Republican Senate is unknown though, and there appears little concern on Obama's part about undermining any remaining ties to congressional Republicans in his final months in office.
His stop in Las Vegas on Sunday kicked off a three-day fundraising tour through San Diego and Los Angeles, where the President was planning to use his still-considerable pull among deep-pocked Democrats to pad his party's congressional campaign coffers, along with the Clinton campaign's.
Already, Obama has appeared in television spots for Democratic Senate candidates in Florida, California, Illinois, North Carolina and Pennsylvania; he's also recorded radio ads for Senate hopefuls in New Hampshire and Nevada. Those states' Senate battles are among the most fiercely contested this year.
Obama has also cut television or radio ads for three governors races and ten House contests, and Democratic officials predict new spots will appear almost daily in other races around the nation.
Democratic officials also said Sunday Obama planned to endorse 150 candidates for state legislatures across the country, lending his voice to recorded phone calls, appearing in television ads, and issuing statements of support in places where his considerable popularity holds sway.
Like his active support for Clinton, Obama's considerable efforts in down-ballot races amounts to an investment in his own legacy, which has relied heavily on executive action prone to reversal by courts or Republican legislatures. In advocating for Democrats in state houses and the US Capitol, Obama is also hoping to ensure his own achievements are furthered -- or at least aren't scrapped -- when he's no longer in office.
A Democratic US Congress could, for example, approve necessary changes to the Affordable Care Act, preventing Obama's signature legislative achievement from collapsing. If Democrats assume a majority in the Senate, the leftward evolution of the federal judiciary begun under Obama could continue, starting with the confirmation of his Supreme Court nominee Merrick Garland (provided Clinton renominates him in January, which is far from a certainty). And instead of relying on Obama's set of broad environmental regulations established through executive action, a Democratic body could write actual laws combating climate change.
In his rally Sunday, Obama declared a loss in November fatal to his presidential record.
"For all the progress we've made, if we don't work as hard as we can in these next 16 days all that progress could be out the window," he said.