Four weeks before the first votes of the 2016 presidential contest, a bizarre year in U.S. politics comes to an end Thursday. With billionaire Donald Trump and Tea Party-aligned Sen. Ted Cruz leading the Republican field, the big question is whether the 2016 election will change American politics as we know it. Six factors to monitor:

 

Cruz loves the trail

Cruz is as comfortable and happy on the stump as he is uptight and gloomy on Capitol Hill. While Republican rivals like Florida Sen. Marco Rubio, former Florida Gov. Jeb Bush and Ohio Gov. John Kasich approach campaigning like a job, Cruz revels in it.

 

Rubio eyes November

Rubio’s pitch to Republican voters is focused on his electability. People who introduce him on the stump make a point to mention it, and the Floridian likes to bring it up. His message of a “new American century” and picking a leader for “tomorrow” previews themes he hopes to use against Democrat Hillary Clinton in the fall.

 

Temperament is key

There are precious few policy disagreements that separate Rubio and Cruz. Temperamentally, however, they’re opposites. While Cruz deploys rhetoric calling for a conservative revolution, Rubio offers a gentler touch in calling for a course correction to preserve the American dream. Cruz is appealing to the hard core conservative wing. Rubio is trying to court the Tea Party base while also appealing to old-school moderates.

 

ISIL and Christie rise

Not coincidentally, support for New Jersey Gov. Chris Christie among Republicans in New Hampshire and nationally has grown since the San Bernardino, Calif., shootings elevated fears of terrorist sleeper cells. “This country is in danger and we need a president who’ll protect the American people,” Christie said recently in Exeter, N.H. “The world is coming apart at the seams, and we can feel it.”

Trump base must vote

Underlying the disaffection among Trump’s predominantly white base are concerns about an economy that has left blue-collar workers behind and about demographic changes that are projected to eventually make whites a minority in the nation. That may account for Trump’s staying power. The million-dollar question in 2016 is whether the estranged and alienated voters Trump has attracted will actually vote.

 

Bush, the anti-Trump

An unexpected twist of 2015 has been the evolution of Bush — a son and brother of former presidents who entered the race as a favorite — into a message candidate. His newly dominant theme: Trump is dangerous and “unhinged,” would be a “chaos president,” and would lose to Clinton.