When U.S. Rep. Joaquin Castro announced earlier this month that he would not run for U.S. Senate in 2020, the San Antonio Democrat cleared up one major question hanging over his party's primary. But the field is anything but settled.

Two weeks later, the clock is ticking for Democrats to mount serious campaigns to unseat U.S. Sen. John Cornyn, R-Texas, an uphill battle even with Texas' changing political landscape. Arguably the most prominent Democrat already running, MJ Hegar, announced her campaign three weeks ago but has been — on the surface, at least — off to a slow start that has done little to dissuade at least three other Democrats from considering runs.

Among them is Amanda Edwards, an at-large Houston City Council member who has been mulling a campaign since at least early March and appears to be moving closer to running. She has been in conversations with the Democratic Senatorial Campaign Committee and is heading to Washington, D.C., next week to continue those discussions, according to a source familiar with her plans.

Edwards, who is African American, has been emphatic that Texas Democrats need a U.S. Senate nominee who can mobilize the party's base, particularly underrepresented groups that suffer the most from low turnout.

"It is imperative — there is no way around it," she told reporters earlier this month in Houston. "If you don't galvanize people of color, young people under the age of 35 ... Democrats are not going to be successful."

In addition to Edwards, state Sen. Royce West, D-Dallas, also continues to draw discussion as a prospective candidate, though he has said he is focused on the ongoing legislative session that ends later this month. And Chris Bell, the former Houston congressman, announced Monday that he was seriously considering a bid. Bell, the 2006 gubernatorial nominee, suggested he was not intimidated by the nascent field, saying competitive primaries can be difficult but healthy in the long run.

"It's sort of like having a family fight, but we all get through Thanksgiving and come together the next day," Bell said, approvingly citing Castro's recent declaration — before he opted against running — that the era of "uncontested primaries in both parties in Texas is over."

While it remains to be seen how viable Edwards, West and Bell would be — Bell is the only one with experience running statewide — they all appear to be undeterred by the opening weeks of Hegar's campaign. Beyond a barrage of fundraising emails, she has kept a low profile, not holding any public campaign events and doing only a handful of media appearances — all things one would expect as a candidate looks to establish early momentum in a nationally watched race.

"It's concerning," said one Democratic strategist unaffiliated with any of the declared or potential candidates. "At this time two years ago, Beto was criss-crossing the state. The question I'm seeing now is where exactly has MJ Hegar been?"

At this point in his blockbuster 2018 campaign, Beto O'Rourke had visited a dozen cities throughout the state and was on his way to hitting twice as many by the end of his first month.

But while O'Rourke's campaign is the comparison most Texans can make to this race, it was not the typical Senate campaign, and Hegar is taking a much more traditional tack. Instead of plowing across the state in a pickup truck and livestreaming dozens of town halls, she has been spending time fundraising and meeting with local activists, working closely with the Democratic Senate campaign arm and her campaign manager, Preston Elliott, a seasoned veteran of Senate races elsewhere in the country.

Elliott had a simple warning for anyone considering taking her on.

"They need to know the size of the fight they’re about ready to get into," he said.

Hegar launched her latest campaign via a web video that invoked the 2018 viral video that vaulted her earlier bid against U.S. Rep. John Carter, R-Round Rock, into competitiveness. The new video also included celebrity endorsements from the previous campaign, a move that rubbed a number of Texas and national Democrats the wrong way — not to mention handed Cornyn's campaign an easy attack line. His campaign has nicknamed her "Hollywood Hegar."

Hegar's campaign manager shrugged off the criticism.

“We are very happy where it ended up," Elliott said. "We had a tremendous response to it, and we got a lot of support. It worked.”

The day after announcing her campaign, Hegar was endorsed by VoteVets, the national progressive group for veterans. Beyond that, other prominent groups are waiting to see how the primary takes shape before potentially getting involved. Among them is EMILY's List, the influential organization that works to elect Democratic women who support abortion rights, which backed Hegar in her U.S. House bid last year and made clear in March that it wanted a woman to challenge Cornyn.

"As of right now, we're closely watching the race," EMILY's List spokeswoman Maeve Coyle said. "We're always thrilled to see women step up and take on these tough flip seats, especially fantastic candidates like MJ."

In addition to Hegar, the Democrats already running include Michael Cooper, Sema Hernandez and Adrian Ocegueda.

Typically, Washington Democrats bristle at competitive U.S. Senate primaries. They often can become bloody affairs, resulting in unelectable candidates who are broke once they win the nomination. But Texas is different from most states.

First of all, it remains a lower priority compared to Senate races in other states, though not as low as it was considered in 2018 — when 10 Democratic senators were running for reelection in states President Donald Trump carried two years earlier. This year, Democrats are in a less defensive position, but other states in contention, like Arizona, North Carolina and Georgia, would be far less expensive for Senate leadership to invest its limited resources.

Even so, O'Rourke's near-ouster of Cruz last fall has changed how the state is viewed ahead of 2020. Key Democrats in Washington are reconsidering whether its 20-plus media markets are worth the investment. And down-ballot, the campaign arm for U.S. House Democrats is threatening to make investments in races in every major media market in the state — an opportunity to offer a reverse coattails benefit to the eventual Democratic nominee running against Cornyn.

Despite the renewed interest in flipping Texas, national Democratic operatives are privately shrugging off the notion of a competitive primary in the state. It is no secret that Texas Democrats have miles to go in building out their party infrastructure, and some argue that several candidates fanning out around the state for nearly a year could accomplish some of that goal.

Yet a crowded Democratic primary sets up the possibility of a primary runoff that won't be settled until next May, leaving the eventual nominee with perhaps three months to replenish a depleted war chest for what is likely to be a multimillion-dollar ad war across Texas airwaves.

For now, Cornyn's campaign is happy to take aim at Hegar as the preferred candidate of Democrats in Washington, D.C., including U.S. Senate Minority Leader Chuck Schumer, D-N.Y.

"It's no surprise that Texas Democrats aren't satisfied with Chuck Schumer's hand-picked candidate and New York politics," Cornyn campaign manager John Jackson said in a statement. "He's forced one candidate out of the race. Is Councilwoman Edwards, Senator West, or Congressman Bell next?"