Republican State Representative Geoff Diehl made it official Tuesday, announcing his candidacy for the U.S. Senate seat currently held by Democrat Elizabeth Warren at an event in his hometown of Whitman.

Speaking to a capacity crowd inside the Whitman VFW, Diehl cast himself as a scrappy conservative underdog capable of ousting Warren next fall.

"We need to secure our borders," Diehl said, beginning an overview of his core beliefs that was punctuated by lengthy bursts of applause. "We need to stop illegal immigration. We need to provide for our veterans and respect law enforcement. We need to cut taxes. We need to grow small businesses and the jobs that come with them."

Diehl cast Warren as an opportunist who’s seeking re-election simply so she can run for president in 2020. He also accused her of actively rooting against President Donald Trump and, by extension, his supporters.

"Job number one for your U.S. senator should not be to hope that the administration fails, and with it the hopes and dreams of Americans across this country who voted for him in November," Diehl said.

Diehl was Trump's campaign co-chair in Massachusetts, and his loyalty to the president could pose a challenge for his candidacy. Gallup puts Trump's approval rating at just 29 percent in Massachusetts, lower than any state except Vermont.

In his speech, Diehl didn't talk up that particular part of his resume. He focused instead instead on his past work rolling back automatic hikes to the state's gas tax and fighting Boston's 2024 Olympic bid.

But afterward, in a press scrum, Diehl insisted that his Trump ties won't be problematic.

"I think people look at me for the record I've had serving on Beacon Hill, and I supported the president because he supported a lot of the things that I've been championing for a long time," Diehl said. "Trying to make sure that, you know, we have secure borders...funds needed for schools, funds needed for law enforcement.... Making sure that we do a better job of providing jobs for the economy, helping small businesses. That's what [Trump's] all about, and that's what my wife and I are all about.

"This is going to be a race about what I can deliver for Massachusetts. And it's not necessarily a referendum on anything other than that."

Diehl joins a crowded field of declared and prospective candidates that includes entrepreneur Shiva Ayyadurai, businessman John Kingston, and Beth Lindstrom, who was a top aide to former Governor Mitt Romney.