President Trump's lack of comment regarding the Austin bombings has not gone unnoticed.

Austin authorities determined Monday that they are dealing with a “serial bomber” terrorizing the city after a Sunday night explosion had “similarities” with the three bombs that detonated in the Texas capital this month.

The Washington Post previously reported:

The explosive device Sunday adds to the uncertainty and tension in Austin, which has been on edge since previous bombings killed two people and injured two others, one seriously. Authorities have seemed at a loss to explain who could be setting off these devices or why, saying only that the bombs were sophisticated and that the attacks could have been motivated by racial bias, although they acknowledged that this is only a theory.

The first victims have been black and Latino in east Austin's historically black and Latino neighborhoods. Two of the black men come from prominent families in Austin's black community, leading some activists to dismiss that the bombings could be coincidental.

Anthony House, 39, was the stepson of Freddie Dixon, a former pastor of Wesley United Methodist Church, a historic church founded at the end of the Civil War by black Americans recently freed from slavery. And Draylen Mason, 19, was the grandson of Norman Mason, owner of a dental practice in the city. His grandmother LaVonne Mason is a co-founder of the Austin-area branch of the National Urban League, a prominent civil rights organization.

Dixon told The Post that he and Norman Mason were close friends and fraternity brothers, and he wondered whether their role in the city's black community played a role in the death.

“It’s not just coincidental,” Dixon said. “Somebody’s done their homework on both of us, and they knew what they were doing.”

“My diagnosis: Number one, I think it’s a hate crime. Number two, somebody’s got some kind of vendetta here,” he added.

Nelson Linder, president of the Austin chapter of the NAACP, shared similar thoughts with theGrio, a news site focusing on issues related to black Americans.

“We think these deaths and bombs have been targeted,” Linder said. “The odds of Anthony being killed, his stepfather being Dr. Dixon, and knowing Draylen’s grandfather? That’s way too many coincidences. How the bombs have been made, how targeted they are, and how they’ve been delivered to peoples’ homes. … this feels personal.”

The third bomb injured Esperanza Herrera, a 75-year-old Hispanic woman who is a neighbor of Erica Mason. Authorities suspect that the package was intended for Mason by someone who assumed she was related to the Mason family.

But the latest incident displays a sudden shift in tactics, said Brian Manley, the interim Austin police chief.

Two white men — one 22, the other 23 — were walking through part of Austin’s southwest area, far from where the first three devices detonated. The explosive device that harmed them was on the side of the road, while the previous packages were all left at people’s homes, authorities said.

“What we have seen now is a significant change from what appeared to be three very targeted attacks to what was, last night, an attack that would have hit a random victim that happened to walk by,” Manley said. “So we’ve definitely seen a change in the method that this suspect … is using.”

While the investigation is ongoing, some have brought attention to the muteness of the president, who campaigned on being tough on terrorists and enforcing public safety.

Donna Brazile, former chair of the Democratic National Committee, used Twitter to ask Trump and other lawmakers what's going on in Texas.

Opinion writer Jamil Smith called the acts terrorism and expressed his hope that Trump will not hinder efforts to get to the bottom of the acts.

And a D.C.-area chapter of the NAACP tweeted that had these bombings occurred in affluent, predominantly white neighborhoods, Trump would have weighed in by now.

Other prominent voices have weighed in on Trump's silence, as well.

After multiple comments, tweets and policies that black Americans have found racially insensitive since Trump launched his campaign, nearly 9 in 10 black Americans have concluded that the president does not value them as much as he does white people, according to a recent Quinnipiac poll. This perception and others like it are contributing to Trump's Gallup approval rating — 11 percent — with black Americans being among his lowest.

Deep concern and anxiety understandably appear to be growing in Austin, particularly in the black community, regarding these bombings. What is not yet clear is how much of a priority this threat to public safety appears to be for the president. As of now, some are concluding that his silence on Twitter and beyond speaks volumes.