While Republicans prepare to welcome Mike Pence as their vice presidential nominee Wednesday night in Cleveland, Hillary Clinton is facing a running-mate dilemma as Democrats get ready for their national convention next week. 

For Clinton, her list of potential vice presidential picks once included a deep bench of feisty candidates all willing to take up the cause. But recent controversies involving several top contenders may be forcing the presumptive Democratic nominee’s hand in eyeing “safer” alternatives – namely Virginia Sen. Tim Kaine and USDA head Tom Vilsack. 

The hits came at a rapid clip this week for others on the short-list. 

One candidate thought to be an early favorite was U.S. Secretary of Housing and Urban Development Julian Castro. But Castro, who met with Clinton in Washington last week, was just cited for violating federal law when he touted Clinton’s candidacy in an April news interview. 

The Wall Street Journal then published a potentially problematic report on another prospect, Labor Secretary Tom Perez, who regularly retells the story of grandfather Rafael Brache being forced to flee the Dominican Republic for opposing the dictatorship of Rafael Trujillo. Perez has praised his grandfather as being “on the right side of history.”

What Perez didn't offer up as often is that his grandfather was one of the dictator’s champions during the first five years of his three-decade rule. 

The Wall Street Journal said Brache also held a string of high-level offices in the Trujillo regime, including being ambassador to the U.S. Brache reportedly “expressed great optimism” for the regime as late as 1935 when political assassinations had been well documented. 

Amid these reports, campaign sources told Fox News that Kaine and Vilsack have emerged as the top two choices for Clinton's running mate. 

Kaine, long rumored to be on Clinton's short-list, still seems to be the leading contender. The former Virginia governor, who represents a key battleground state, is considered a safe choice for Clinton, someone who could help her appeal to moderates who have been turned off by Trump's rhetoric.

However, Vilsack, a former Iowa governor who is a longtime friend of the Clintons, is being described as a "strong" second choice. 

This suggests Clinton may also be leaning away from Massachusetts Sen. Elizabeth Warren, the firebrand liberal icon who also has the potential to turn off independent voters. 

Republican strategist Jim Dornan called Kaine a "safe pick" -- and not a bad idea.  

“I’d be a lot more worried about Elizabeth Warren,” said Dornan, senior vice president at Artemis Strategies. “Pence and Kaine balance out the tickets very well. They are both the same in terms of temperament.”

While a Clinton-Warren matchup might provide more political fireworks, Dornan warned “it might be almost too combustible” and says Kaine would be the better bet.

An Ohio-based Democratic strategist told FoxNews.com that the controversies popping up around Clinton’s list of candidates going into next week’s Democratic National Convention is actually making the job of finding the right fit for the ticket much easier. 

“The media is vetting the candidates for her,” the strategist told FoxNews.com. “They are doing her job.”

Castro's problems stemmed from touting Clinton in an interview earlier this year. 

“Clinton is the most experienced, thoughtful and prepared candidate for president that we have this year,” Castro had said. Though he said he was “taking off” his “HUD hat for a second and just speaking individually,” the Office of Special Counsel said he violated the Hatch Act.

The Act forbids anyone in the executive branch – other than the president and vice president – from using his or her official position to engage in political activity.

It doesn't get better for Warren, who was once thought to be a strong contender for the No. 2 slot. The popular liberal senator has in recent weeks engaged in Twitter tirades against Republican nominee Donald Trump and Pence.

On July 16, she tweeted: “Of COURSE @realDonaldTrump – a guy who calls women fat pigs & bimbos – picked a VP who is famous for trying to control women’s bodies.”

A minute later she tweeted, “@realDonaldTrump & @mike_pence are a perfect match: Two small, insecure, weak men who use hate & fear to divide our country & our people.”

Dornan said: “To be honest, the White House isn’t big enough to house both [Clinton and Warren’s] egos.” 

Some Democratic sources have told Fox News that Trump's selection of Pence as his running mate has cleared the way for Clinton to pick a similarly low-key candidate for vice president.

During an interview with Charlie Rose on Monday, Clinton emphasized “experience” would be key in determining who will be on her ticket.

When Rose specially asked about Kaine, who has called his own personality “boring,” Clinton responded: “I love that about him. I mean, he’s never lost an election. He was a world-class mayor, governor and senator, and is one of the most highly respected senators I know.”

Fox News' Jennifer Griffin contributed to this report.