EXCLUSIVE: Speaker Mike Johnson, R‑La., is embarking on a 20-state tour this month to campaign for House Republicans and GOP candidates across the country, Fox News Digital has learned, in a bid to keep hold of his majority in November.Johnson will be visiting key districts in Wisconsin, Arizona, Ohio, Montana, Colorado, New Mexico, Virginia, Connecticut and other states to meet with candidates and fundraise. Republicans have been rushing to recalibrate after President Biden dropped out of the White House race just two weeks ago, effectively anointing Vice President Kamala Harris as his successor.Harris is now set to embark on her own battleground state blitz beginni …