Johnson faces a tough re-election battle in 2016 against Russ Feingold.
Jim Ruvolo, the former chairman of the Ohio Democratic Party, is openly warring with David Pepper, the current chairman, accusing him of trying to intimidate a Democrat running for Senate into leaving the race.
The new poll shows the incumbent Republican senator ahead by 6 points.
Some Democrats see Kate McGinty as a stronger challenger to the Republican incumbent.
Rep. David Jolly (R-Fla.) said he will reject the "politics of division and class warfare."
The business group is backing GOP Sen. Mark Kirk in Illinois.
Carlos López-Cantera is pitching himself as a Washington outsider.
State Sen. Kelli Ward would likely struggle to compete with the five-term senator's campaign.
Martin Matishak 07/13/15 10:04 AM EDT
Arizona state Sen. Kelli Ward will announce her plans at a "major event" on Tuesday.
A DSCC memo first obtained by The Hill says Sen. Richard Burr is untested.