WASHINGTON — As Donald J. Trump prepared to take his beauty pageant to Moscow in 2013, he relished the participation of one man above all: President Vladimir V. Putin. “Do you think Putin will be going to The Miss Universe Pageant in November in Moscow — if so, will he become my new best friend?” he wrote on Twitter.
Mr. Putin did not attend — in fact, Mr. Trump has yet to meet him, by all accounts — but his admiration for the Russian leader, shared by some of his campaign advisers, is clear. It stems from an affinity for brash, swaggering politics and business dealings in Russia that has overturned decades of Republican orthodoxy about Russia and its leader as an aggressive authoritarian whose values are inimical to those of the United States.
Hillary Clinton, by contrast, has a far more contentious history with Mr. Putin, despite the “reset” President Obama’s administration pursued with Russia during her tenure as secretary of state. In 2011, Mr. Putin accused her of instigating the huge protests that erupted after parliamentary elections marred by fraud.
“She set the tone for some actors in our country and gave them a signal,” he said darkly, going on to accuse her of engaging in “active work,” an old term of art for covert K.G.B. operations. When she compared Russia’s intervention in Ukraine to Hitler’s moves in the 1930s, he said she had “never been too graceful with her statements.”
Now the question has emerged in the United States election campaign whether Mr. Putin has opted — directly or covertly — to throw Russia’s support behind Mr. Trump. The conclusion by cybersecurity experts that Russian intelligence agencies breached the Democratic National Committee and released thousands of emails on the eve of the party’s convention prompted accusations from Democrats and some Republicans that Mr. Trump was a kind of “Siberian candidate,” bolstered from abroad to undermine the nation.
“Given Donald Trump’s well-known admiration for Putin and his belittling of NATO, the Russians have both the means and the motive to engage in a hack of the D.N.C. and the dump of its emails prior to the Democratic convention,” Rep. Adam Schiff of California, a Democrat who is the ranking member of the House Permanent Select Committee on Intelligence, said in a statement on Monday.
“That foreign actors may be trying to influence our election — let alone a powerful adversary like Russia — should concern all Americans of any party,” he added.
Mr. Trump dismissed the idea as a joke, and his campaign chairman, Paul Manafort, called it “crazy” in remarks broadcast on CNN. “I don’t even know what you’re talking about,” he said.
Just four years ago, the Republican presidential candidate Mitt Romney called Russia the No. 1 geopolitical threat to the United States, a remark that was criticized at the time by Democrats but that seemed to anticipate the souring of relations after the annexation of Crimea from Ukraine in 2014.
As her campaign approached, Mrs. Clinton, too, sharpened her tone on the threat Mr. Putin posed, distancing herself in her book “Hard Choices” from a “reset” widely seen as a failure. Now it is Mr. Trump who sees — though not always — a new era of cooperation, “because Putin likes me,” as he put it on Twitter.
Mr. Trump’s dabbling in business in the country dates to the Soviet era, when he visited Moscow in 1987 at the invitation of the Soviet ambassador to the United States, Yuri Dubinin, who had mentioned at a lunch in New York that his daughter had admired Trump Tower. “He actually suggested that we make a similar statement in Moscow,” Mr. Trump said at the time.
Mr. Trump’s plans for a Trump Tower in Russia never came to fruition, but his interest in the country as a potential investment and marketing opportunity never waned entirely, as his decision to stage the Miss Universe pageant at a concert hall in one of Moscow’s deluxe shopping centers, Crocus City, demonstrated.
As his campaign took shape this year, he turned to advisers who shared his views on Russia. Mr. Manafort has had extensive financial and political dealings with business executives in Russia and Ukraine.
Beginning in 2005, he worked as a political strategist in Ukraine for Viktor Yanukovych and his Party of Regions, which struggled to regain power after his first election as president in late 2004 was overturned as fraudulent, in what became known as the Orange Revolution. According to one of several cables disclosed by WikiLeaks in 2010, Mr. Yanukovych told the American ambassador at the time that he intended to “build Regions into a party that had a platform and policies.”
“Doing so was important for the development of democracy in Ukraine, he asserted,” according to the cable. Mr. Yanukovych won the presidency in 2010, only to be ousted in the political upheaval that prompted the Russian intervention in Crimea and later in eastern Ukraine.
Mr. Manafort also had business investments in the region, some of which were detailed in a lawsuit filed in New York in 2011 by Mr. Yanukovych’s rival, Yulia Tymoshenko. Although the suit was dismissed, it detailed connections with a Ukrainian gas middleman, Dmytro Firtash, and a reputed kingpin of the Russian mob, Semyon Y. Mogilevich, as well as with another Russian tycoon, Oleg Deripaska.
In the lawsuit, Ms. Tymoshenko claimed that Mr. Manafort had helped Mr. Firtash in a project to use illicit proceeds from gas deals to buy and redevelop the former Drake Hotel on Park Avenue in Manhattan. The United States tried to extradite Mr. Firtash from Austria, but the request was turned down in 2015.
Adrian Karatnycky, an expert on Ukraine at the Atlantic Council, said that he viewed Mr. Manafort as a canny strategist and businessman. “I don’t see Manafort going in as an agent of Russian imperialism, but of personal opportunism,” he said.
Another adviser to Mr. Trump’s campaign, Carter Page, also lived and worked in Russia, serving as a consultant with Gazprom, the state-owned energy giant. In July, he delivered a graduation speech at the New Economic School in Moscow in which he warned that hostility between the United States and Russia, reminiscent of the Cold War, was a mistake.
While Mr. Putin has scrupulously avoided endorsing either candidate in the United States campaign, the tenor of coverage by the state news media has clearly favored Mr. Trump. He is portrayed as a populist break from the past, while from Russia’s point of view, Mrs. Clinton embodies the worst aspects of an aggressive, antagonistic American establishment.
“They don’t really expect much from a Clinton presidency other than continued confrontation, while they view a Trump presidency as a window for improved relations,” said Vladimir Frolov, the foreign affairs columnist for the online magazine Slon.ru.
A report on Sunday on the weekly television program Vesti Nedeli cited an interview with The New York Times in which Mr. Trump suggested that American protection for the Baltic nations would not be automatic if he were elected, despite the collective defense clause in the NATO treaty.
“Such a practical look at the alliance shocked the American establishment, for whom NATO has long been a cult, as it is the main instrument of the U.S. for dominance in Europe,” the television report asserted, showing photographs of American headlines calling Mr. Trump an agent and lap dog of Mr. Putin.
In December, when Mr. Trump’s candidacy was still relatively young, Mr. Putin praised him, when asked, as flamboyant and talented. In a more recent appearance, at the St. Petersburg International Economic Forum, he welcomed Mr. Trump’s stated goal of improving relations. “What’s wrong with that?” Mr. Putin said, prompting applause from an audience that included business executives eager to resume smooth economic relations.
Mr. Trump has boasted about Mr. Putin’s flattery, but his remarks on Twitter have been far from consistently positive toward the Russian leader. “What do you think Obama will do when Putin seizes Alaska?” he posted in March 2014, days after the annexation of Crimea. A month later, he quoted an evident admirer: “President Trump, now that would make Putin wet himself!”
An irony for Russia, of course, is that interference in another country’s political process is precisely what Mr. Putin has accused the United States of doing for at least the last 12 years.
Matthew Rojansky, the director of the Kennan Institute at the Woodrow Wilson International Center for Scholars, said that while it was plausible that Russian intelligence agencies were behind the breach and leaked the emails, it did not necessarily follow that Moscow had a favorite.
He said the leak more likely would reflect a goal “to stir the pot,” as Russia has done with support of insurgent parties in Europe. Mr. Putin, he said, had to be aware that direct intervention could well backfire with American voters, especially those in swing states like Ohio and Pennsylvania with roots in Poland, Ukraine or the Baltics.
“Could Putin really be that stupid?” he asked.
Steven Lee Myers reported from Washington, and Neil MacFarquhar from Moscow. Andrew E. Kramer contributed reporting from Moscow, David M. Herszenhorn from Washington, and Doris Burke from New York.