With most predicting he will go down in defeat, Democratic Sen. Russ Feingold earned compliments from his former GOP ally, Sen. John McCainJohn Sidney McCainEx-McSally aide pleads guilty to stealing over 0K in campaign funds DOJ: Arizona recount could violate civil rights laws Cheney fight stokes cries of GOP double standard for women MORE, on Monday.

The Arizona senator and 2008 GOP presidential nominee has campaigned hard for Republican Senate candidates this cycle while sharply criticizing their Democratic rivals, such as Sens. Barbara BoxerBarbara Levy BoxerBottom line Trump administration halting imports of cotton, tomatoes from Uighur region of China Biden inaugural committee to refund former senator's donation due to foreign agent status MORE (Calif.) and Patty MurrayPatricia (Patty) Lynn MurraySchumer 'exploring' passing immigration unilaterally if talks unravel Senate Democrats push Biden over raising refugee cap House passes bill to combat gender pay gap MORE (Wash.) But McCain saved kind words for Feingold (Wis.), with whom he worked on landmark campaign finance reform legislation eight years ago.

Asked on Fox News if he feels bad when his Senate colleagues lose, McCain said, "Yes, and if I may say so, I've grown to have the greatest respect and affection for my friend, Russ Feingold. He's an honest man, a man of great integrity, and I've grown to appreciate him more than ever. And it looks like he might be a casualty tomorrow."

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McCain has taken his lumps from critics ever since his presidential campaign for moving to the right instead of championing his bipartisan work in the upper chamber with members like Feingold. 

Now the three-term Wisconsin senator is poised to lose to upstart GOP candidate Ron JohnsonRonald (Ron) Harold JohnsonSunday shows preview: Coronavirus dominates as White House continues to push vaccination effort Overnight Health Care: WHO-backed Covax gets a boost from Moderna Vaccine hesitancy among lawmakers slows return to normalcy on Capitol Hill MORE, who leads by high single digits in most polls.

Johnson did not receive an endorsement from McCain, nor did the Arizona senator donate to his campaign.

McCain in January decried the Citizens United Supreme Court decision for knocking down much of the law he passed with Feingold. But so far he has not signed on to legislation requiring greater disclosure for corporate and union political spending.