President Barack Obama called the fractious Republican primary race a "crack-up" and rejected any suggestion that it is a consequence of actions he has taken.

Obama weighed in on the 2016 presidential campaign during a news conference with Prime Minister Justin Trudeau at the White House on Thursday.

Obama said Donald Trump's positions aren't different from those of the other Republican presidential candidates — he's just more provocative in talking about them. Obama said Trump's positions on immigration and other issues aren't that different from those of Texas Senator Ted Cruz or Florida Senator Marco Rubio.

Obama called the GOP primary a "circus" and a "Republican crack-up" resulting from GOP actions. Obama said he takes responsibility for failing to bridge political divides, but says he has not contributed to the worsening tone of political rhetoric.

He said he believes the Democrats are doing a fine job of working out issues in their primary.

Also Thursday, Obama said he's holding out hope that "cooler heads will prevail" and Republicans will back down from their plan to block his Supreme Court nominee. 

He said he's looking for a candidate with "humility," who doesn't make policy from the bench, and someone who recognizes the role judges play in protecting minorities.
 
Obama's top tier of candidates include Judge Sri Srinivasan of U.S. Court of Appeals for the District of Columbia Circuit, Merrick Garland, chief judge on same court, and Judge Paul Watford of the 9th U.S. Circuit Court of Appeals, according to a source familiar with the selection process. Ketanji Brown Jackson, a D.C. district court judge, is also under consideration, although a less likely option, said the source, who asked not to be identified because the person was not authorized to publicly discuss private White House deliberations.

With files from CBC News