Elizabeth Warren has enjoyed a heady summer of massive crowds and endless selfie lines as she steadily climbs in Democratic presidential primary polls. With the apparent success comes a new reality: She's now a prime target for rivals and their supporters. Some of the offensives are direct, with Pete Buttigieg hammering her this week as 'evasive' on what a single-payer government health insurance system would mean for middle-class tax bills. Some Bernie Sanders supporters lashed out when the Working Families Party endorsed Warren over Sanders. Others are more circumspect, with Joe Biden's campaign beginning to question Warren's corporate legal work decades ago, suggesting it's at odds with her brand as a progressive champion for middle-class Americans. Together, it's a new dynamic that at once affirms Warren's strength and promises to test whether she can dispatch fellow progressive Bernie Sanders and ultimately challenge the more moderate Biden, who has maintained front-runner status since the spring. At least in the short term, it could shift some heat off of Biden, who as the consistent polling leader has drawn more frequent attacks and media scrutiny than the Massachusetts senator, but has thus far weathered the hits. For her part, Warren insists she won't go hard after her opponents, at least not yet, and her campaign has declined comment on the emerging onslaught. Some of her supporters, meanwhile, are leaning into the latest turn. 'Ironically, I think most attacks make her stronger, because they send a signal to Democratic voters that she's a threat and can win,' said Adam Green, co-founder of the Progressive Change Campaign Committee and top Warren supporter. 'That's a far cry from January.' Mayor Pete Buttigieg, who along with Kamala Harris is trying to join a top tier that now consists of Warren, Sanders and Biden, launched the most direct attacks this week, casting her as less-than-honest about how she'd pay for the 'Medicare for All' insurance overhaul. Buttigieg, like Biden, backs adding a government insurance plan to existing insurance markets without eliminating private insurance. Buttigieg told CNN that Warren has been 'extremely evasive' when asked about middle-class taxes that Sanders, the lead 'Medicare for All' advocate, has said would have to go up. Warren emphasizes that many if not most middle-class households would see their overall spending on health care go down, because they'd no longer have private premiums, deductibles and co-pays. But she avoids confirming that taxes would rise. 'Look, people are used to Washington politicians not giving straight answers to simple questions,' Buttigieg said in a remark striking at Warren's effort to frame herself as an outsider and reformer. Buttigieg's argument partially echoes a months-old Biden tactic. 'At least Bernie is being honest,' Biden would often say. He got more direct Friday in Iowa. 'Tell Elizabeth ... she's gonna raise people's taxes,' he said at a campaign stop in Cedar Rapids. 'What we are gonna do' if we end up in a recession, he added. Harris hasn't yet taken on Warren, but in a conference call with reporters this week, a top Harris aide took veiled swipes at the progressives. 'I think there are far more ideological, strict ideological candidates who I believe will contribute to the partisan rancor,' Lily Adams said. One of Biden's top supporters, meanwhile, has abandoned all subtlety. 'I like Elizabeth Warren. I like her a lot. Too bad she's a hypocrite,' Ed Rendell wrote in a Washington Post op-ed this month. He chided the senator for touting her refusal to hold traditional large-donor fundraisers when she's previously taken big donor money — most recently ahead of the 2018 midterms — and used her Senate campaign account to seed her presidential run. It's an argument related to one Biden and his aides make more quietly: that Warren is glossing over her time as a Republican who did legal work for the kinds of large corporations she now blasts. Biden has yet to make that case explicitly, perhaps aware of his own cozy history with credit-card companies in his home state of Delaware and Warren's previous criticism of it. But his aides noted ahead of the Sept. 12 Houston debate that he's released at least two decades of his tax returns, more than Warren, and they suggested she doesn't want scrutiny on her sources of income in the years before she established herself as a consumer champion. At a Houston fundraiser the day after debate, Biden quipped that some of his opponents used to be Republicans. Green said he welcomes Biden to make those claims openly. 'Elizabeth Warren's willingness to challenge corporate power is unquestioned,' Green said. 'He'd only help her emphasize her record.' Whatever the case, the shifting spotlight could help Biden in the short run. Since he entered the race in April, Biden, 76, has had to defend his long public record, deflect a stream of broadsides during debates and, in part because of his own verbal missteps, navigate questions about whether he's still up for the job — concerns the 70-year-old Warren hasn't faced. Biden's aides say candidates are ratcheting up their shots at Warren because previous attempts to derail Biden haven't yet worked. 'I think candidates have seen ... that attacking Joe Biden is not the way to advance yourself,' said Kate Bedingfield, a top Biden campaign official, after the Houston debate. Indeed, over the first three debates, Harris, Bill de Blasio, Eric Swallwell and Julian Castro blistered Biden on everything from his record on school desegregation and immigration to his fitness for office. Swallwell and de Blasio have since dropped out. Castro is mired near the bottom of the polls. Harris is struggling to establish herself as a top tier candidate. Now, if nothing else, candidates like Buttigieg who focus attention on Warren aren't spending energy on Biden. ___ Associated Press reporters Thomas Beaumont in Des Moines, Iowa, Alexandra Jaffe in Cedar Rapids, Iowa, and Juana Summers in Washington contributed. ---- Follow Barrow on Twitter at https://twitter.com/BillBarrowAP .