MORGANTOWN, WV - MARCH 01:  Republican candidate for U.S. Senate Don Blankenship speaks at a town hall meeting at West Virginia University on March 1, 2018 in Morgantown, West Virginia. Blankenship is the former chief executive of the Massey Energy Company where an explosion in the Upper Big Branch coal mine killed 29 men in 2010.  Blankenship, a controversial candidate in central Appalachia coal country, served a one-year sentence for conspiracy to violate mine safety laws and has continued to blame the government for the accident despite investigators findings.  (Photo by Spencer Platt/Getty Images)
PHOTO: Spencer Platt/Getty Images North America/Getty Images
MORGANTOWN, WV - MARCH 01: Republican candidate for U.S. Senate Don Blankenship speaks at a town hall meeting at West Virginia University on March 1, 2018 in Morgantown, West Virginia. Blankenship is the former chief executive of the Massey Energy Company where an explosion in the Upper Big Branch coal mine killed 29 men in 2010. Blankenship, a controversial candidate in central Appalachia coal country, served a one-year sentence for conspiracy to violate mine safety laws and has continued to blame the government for the accident despite investigators findings. (Photo by Spencer Platt/Getty Images)
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MORGANTOWN, WV - MARCH 01:  Republican candidate for U.S. Senate Don Blankenship speaks at a town hall meeting at West Virginia University on March 1, 2018 in Morgantown, West Virginia. Blankenship is the former chief executive of the Massey Energy Company where an explosion in the Upper Big Branch coal mine killed 29 men in 2010.  Blankenship, a controversial candidate in central Appalachia coal country, served a one-year sentence for conspiracy to violate mine safety laws and has continued to blame the government for the accident despite investigators findings.  (Photo by Spencer Platt/Getty Images)
PHOTO: Spencer Platt/Getty Images North America/Getty Images
MORGANTOWN, WV - MARCH 01: Republican candidate for U.S. Senate Don Blankenship speaks at a town hall meeting at West Virginia University on March 1, 2018 in Morgantown, West Virginia. Blankenship is the former chief executive of the Massey Energy Company where an explosion in the Upper Big Branch coal mine killed 29 men in 2010. Blankenship, a controversial candidate in central Appalachia coal country, served a one-year sentence for conspiracy to violate mine safety laws and has continued to blame the government for the accident despite investigators findings. (Photo by Spencer Platt/Getty Images)
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(CNN) —  

The Republicans’ bid to keep or expand their majority in the Senate starts Tuesday in West Virginia, Indiana and Ohio, with hotly contested primaries to take on three of the nation’s most endangered Democratic incumbents.

The political world will be watching West Virginia to see if Don Blankenship – the ex-convict coal baron whose late surge has Senate Majority Leader Mitch McConnell’s allies fretting that he could spoil the party’s chances of unseating Democratic Sen. Joe Manchin there this fall – defeats Attorney General Patrick Morrisey and Rep. Evan Jenkins.

“Let’s just hope and pray that doesn’t happen,” South Dakota’s Sen. John Thune, the No. 3-ranking Senate Republican, told reporters after a meeting in McConnell’s office Monday afternoon.

“It wouldn’t be good,” he added.

In Indiana, self-funding former state Rep. Mike Braun, a shirtsleeve-wearing businessman, takes on the two men his campaign ads have cast as cardboard cutouts: Reps. Todd Rokita and Luke Messer.

Messer and Rokita sprinted to the finish line hammering Braun over his history prior to 2012 of voting in Democratic primaries. But Braun has pumped nearly $6 million of his own money into the race, allowing him to outpace his rivals in TV ads.

The winner will take on Sen. Joe Donnelly in what could be the GOP’s best chance of picking off a Democratic-held seat.

In Ohio, a little-watched race between Rep. Jim Renacci and the self-funding Mike Gibbons will determine who takes on Sen. Sherrod Brown in a state that President Donald Trump won by 9 percentage points in 2016.

Trump has loomed large in all three races as they come down to the wire.

In West Virginia, he weighed in Monday morning on Twitter, urging voters to back either Morrisey or Jenkins over Blankenship.

He tweeted: “To the great people of West Virginia we have, together, a really great chance to keep making a big difference. Problem is, Don Blankenship, currently running for Senate, can’t win the General Election in your State…No way! Remember Alabama. Vote Rep. Jenkins or A.G. Morrisey!”

Blankenship is the most controversial GOP candidate since the one Trump alluded to: Alabama’s Roy Moore, who lost a Senate race in the deep-red state in December.

Blankenship’s year in prison after a conviction related to the collapse of the Upper Big Branch Mine, which killed 29 miners in 2010, has made him a prime target. And his ads assailing McConnell as “Cocaine Mitch” (over a bust on his father-in-law’s shipping company) and his “China family” have infuriated the Kentucky Republican’s allies.

In Indiana, Trump hasn’t weighed in against any individual candidate – and all three have done everything they can to cozy up to him.

Among their gestures: Messer led a group of House Republicans who nominated Trump for the Nobel Peace Prize over his handling of North Korea, and Rokita said he’d file a resolution to end the “witch hunt” led by special counsel Robert Mueller.

In Ohio, gubernatorial primaries are the main event.

On the Democratic side, Richard Cordray, the former Consumer Financial Protection Bureau head, faces Bernie Sanders-backed former Rep. Dennis Kucinich. For the Republicans, Attorney General Mike DeWine faces Lt. Gov. Mary Taylor.

House races in Ohio and North Carolina will also get attention on election night.

In Ohio, the primaries for former GOP Rep. Pat Tiberi’s 12th District seat will set up a potentially competitive August special election. In North Carolina, Republican Reps. Robert Pittenger and Walter Jones are attempting to fend off primary challenges.