Donald Trump has stressed that he wants to pick a vice presidential candidate with close ties to the Congress, believing that this would be the best way to get his agenda passed into law.

He may have to alter that notion.

Two more top V.P. prospects have withdrawn their names from consideration, leaving a short list of potential V.P. candidates that might have the stature to assure congressional Republicans.  Freshman Iowa senator Joni Ernst and Senator Bob Corker of Tennessee took their names off Trump's list in the last 48 hours, narrowing Trump's choices. 

Politico:

The withdrawals Wednesday further depressed Senate Republicans who are still looking for some measure of reassurance from Trump’s unrelenting campaign controversies and who thought his choice for running mate could be a soothing gesture.

“I don’t need to say any more about the campaign,” said Sen. Jeff Flake (R-Ariz.), who added that it was disappointing Corker and Ernst declined to be considered. “I understand their reluctance, I’ll put it that way.”

Trump and his GOP critics agree on one thing: A vice-presidential candidate familiar with Congress and the ways of Washington would be a major boost to his campaign. Former Speaker Newt Gingrich would meet that threshold, though it’s been nearly two decades since he left Congress. Republicans on Capitol Hill are pushing harder for an active legislator, which is why Ernst and Cotton found themselves the subject of intense public lobbying by their colleagues.

The fact that Trump met this week with Ernst and campaigned with Corker was enough to buck up some Republicans, but their encouragement lasted barely a day.

Before Ernst all but withdrew from the veepstakes in an interview with Politico, Sen. Dean Heller of Nevada posed a question to her that underscored his and other Republicans’ current reluctance with Trump.

“I asked her today if I could vote for her and against Trump. Because I’m for her, I’m for Cotton,” said Heller, who has not endorsed Trump. “Who he selects for vice president does make a difference.”

But Republicans being floated for the No. 2 post — particularly those who could run for president themselves in the future — face a tough call. They’re weighing the call of duty to the Republican Party against stepping into the great unknown of being forever associated with Trump.

Corker alluded to that challenge on Wednesday. The Tennessee senator noted that he has offered “some constructive observations” publicly for Trump throughout the real estate mogul’s unpredictable campaign — an advisory role that Corker acknowledged would not be possible as his running mate.

“Everybody’s going to be thinking about that. And they should be,” Sen. John Thune (R-S.D.) said. “But I think ultimately the question is going to be, in the minds of people who are probably on that narrow list: ‘What can I do to help the country? What can I do to elect a Republican president in November?’”

The impact of a vice presidential pick is overblown, in my opinion.  It never rises to the level of the hype generated and ends up being a media-driven story more than a genuine indication of how a candidate thinks.

Unless the presumptive nominee has trouble filling the second slot with the person he wants.  Then it becomes a legitimate issue.

There is no lack of candidates eager to run with Trump, so it's not as though he's going to be picking from the bottom of the barrel.  But the reluctance of sitting politicians to have their names so closely associated with the nominee does not bode well for GOP unity or for victory in November.