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One thing that's striking about the presidential race, which, finally, officially begins soon, is how much the race has been shaped by Barack Obama. The course of the contests for both the Republican and Democratic nominations would be inconceivable absent the course of the Obama presidency.

This is most apparent in the phenomenon that goes by the name of Donald Trump. Trump's gratuitous insults of rivals reflect the coarseness of Obama's nonstop insults of Republicans and anyone who does not share his views and priorities. Despite his pre-presidential promises of nonpartisanship, Obama has been the most grating and vitriolic partisan president of the last 60 years.

Trump's more outlandish proposals -- making Mexico pay for a border wall, making common cause with Russia in Syria -- can be seen as a variation on Obama's insistence that climate change is the nation's No. 1 problem and his acquiescence in, well, making common cause with Russia in Syria.

And the adoring crowds that throng Trump's monster rallies, what do they remind you of? The crowds that cheered Obama in 2008 as he promised to fundamentally transform America and stop the rise of seas.

The Republicans who have emerged as Trump's chief rivals, Marco Rubio and Ted Cruz, had interesting beyond-the-Beltway careers pre-2008 (Rubio in the Florida legislature, Cruz in the Texas attorney general's office) but emerged as national figures only after Obama's inauguration.

Both won upset victories against established figures in open Senate races. In 2010 Rubio challenged Gov. Charlie Crist, who famously hugged Obama in February 2009, forced him out of the Republican primary and beat him handily in the three-way general. In 2012 Cruz challenged Lt. Gov. David Dewhurst, held him under 50 percent in the primary and then won the runoff and general election.

Thus both these freshman senators got elected from the nation's third and second largest states as Obama opponents. Their differences on immigration and foreign policy are framed as arguments over which one is more anti-Obama.

So Trump, never a political candidate until 2015, and Rubio and Cruz, unknowns nationally six years ago, have been far more successful at engaging the attention and winning the support of Republican caucus-goers and primary voters than have rivals with greater but -- since they have not held public office since 2006 -- less recent achievements.

Jeb Bush is the prime example. I used to write that he was the most effective conservative governor in the last dozen years; now I have to delete "dozen" and substitute "20." Today's Republicans seem uninterested in Bush's genuinely impressive record in Florida. They're troubled by his current support of Common Core, which he sees as imposing rigor but they see as imposing liberal mushiness, and by his conviction that massive low-skill Latin immigration benefits the nation.

Even further down the pack are the last two Iowa caucus winners: Mike Huckabee, who didn't run for re-election as governor of Arkansas in 2006, and Rick Santorum, who was defeated badly for re-election in Pennsylvania that year.

Republican voters seem less interested in John Kasich's conservative achievements as House Budget chairman in the 1990s than his support of Obama's Medicaid expansion in 2014. Chris Christie has gained ground by campaigning on his pre-2008 record as U.S. attorney and ignoring his post-2008 record as governor of New Jersey.

On the Democratic side, Hillary Clinton's career predates the Obama presidency by a lot. At Yale Law she worked for Joe Duffey's Senate campaign in the election of 1970, when Obama was nine and Rubio and Cruz were not yet born.

But this year Clinton is running more on, or to the left of, the platform of Obama (who has 44 percent job approval) than on that of Bill Clinton (who left office with 65 percent job approval). She is obviously, though not particularly deftly, responding to a leftward lurch among Democratic voters, an impulse often seen in the final years of Democratic administrations: See Gene McCarthy in 1968, Ted Kennedy in 1980, Ralph Nader in 2000 and Bernie Sanders in 2016.

Clinton hopes to replicate Obama's 51 percent coalition at a time when partisan preferences have been stubbornly stable for two decades. But turnout generally has been falling during the Obama presidency; Clinton is unlikely to match Obama's turnout and percentage numbers among blacks, and Republican debate viewership has set new records. It's possible that the Obama presidency, having reshaped the nomination contests, may be reshaping the general electorate -- and not to Democrats' benefit.