PHILADELPHIA -- The massive email hack on the Democratic National Committee, purportedly by Russian government agents, has drawn new and unwanted attention to longstanding ties between Republican presidential nominee Donald Trump and Russian business interests.

“The hack at least seems to have come from Russian government entities, specifically from some of their military intelligence communities,” John Podesta, Hillary Clinton’s campaign chairman, told ABC News Monday. “So that’s very worrisome. Whether they’re actively trying to interfere in the U.S. election, that’s something that I guess we’ll need to see.”

Clinton presidential campaign manager Robby Mook went further on ABC News’ “This Week” Sunday, saying that “experts” told his team that “this was done by the Russians for the purpose of helping Donald Trump.”

Trump speculated in a speech Monday that “China, Russia or one of our many, many friends… hacked the hell out of us,” but the GOP candidate and his top advisers have rejected the suggestion that the Russians were motivated to help the business mogul. Trump tweeted Monday morning prior to his speech, “The new joke in town is that Russia leaked the disastrous DNC e-mails … because Putin likes me.”

Suspicions about the Russian interest in Trump’s candidacy stem in part from the Republican businessman’s comments and long history of work with Russian business interests. Trump has long hinted that he would have a warm relationship with Russian President Vladimir Putin.

“Putin hates us. He hates [Barack] Obama. He doesn’t hate [me],” Trump told reporters last fall. “I think he’d like me. I think I’d get along great with him, if you want to know the truth.”

Trump has made repeated trips to Russia, including in 2013, when a Russian billionaire bought the rights to host the Miss Universe pageant. Sergio Millian, a Russian consultant based in New York, told ABC News that during that trip he helped arrange a series of meetings between Trump and Russian businessmen.

“My colleagues and I helped arrange presentations at the Millionaire Fair in Moscow that featured billionaires and multimillionaires,” Millian said. “He met primarily with businesspeople, with several billionaires.”

Trump spent the most time, Millian said, with the Russian real estate tycoon Aras Agalarov, who heads the firm Crocus International. “He was one of those who the conversation was going on for a long time,” Millian said.

Trump started exploring real estate options in Russia in the 1990s, touring Moscow with close friend Howard Lorber. A real estate developer who has done business there, Lorber appeared during the Republican National Convention in the biographical video of Trump that appeared on jumbotrons before his acceptance speech.

Carter Page, an energy expert Trump tapped as a foreign policy adviser, spent three years living in Moscow working on key transactions with Gazprom, a Russian oil giant that is largely state owned. Page was in Moscow last month to give a speech at a Russian business school.

“If you don’t treat others with respect, they won’t treat you with respect,” he told the audience. “This applies not only on the personal level in the daily lives of individuals but especially when we venture out into the international arena and any level of interaction. Respect is not something which magically appears, but rather it needs to be earned on both sides of a relationship, often through a lot of hard work amidst very difficult negotiations.”

More recently, speculation about Trump’s posture toward Russia surfaced after two members of the Platform Committee at the Republican convention in Cleveland were quoted in The Washington Post questioning why the Trump campaign watered down a pledge to give Ukraine weapons to fend off Russian aggression. The new language pushed by Trump officials eliminated the GOP’s call for “providing lethal defensive weapons.” Instead, the platform calls for providing Ukraine with “appropriate assistance.”

Trump’s campaign manager, Paul Manafort, who did consulting work in Ukraine for a political candidate with Russian ties, dismissed outright the notion that Russian hackers were looking to help the Republican nominee.

Asked by George Stephanopoulos on ABC News’ “This Week” on Sunday if there were any ties between Trump’s campaign and Putin, Manafort said, “No, there are not. That’s absurd. And you know, there’s no basis to it.”