Next week, Democrats will be rallying for Representative Ruben Gallego and against someone who used to be one of their own — the newly independent senator of Arizona, Kyrsten Sinema.

The event, hosted by the Replace Sinema PAC, is billed as “a reception to kick off the 2024 election cycle” and will feature big names in the Democratic Party, including Speaker Pelosi and Congressman Dan Goldman.

The event, though, comes as the 2024 election cycle for the Senate race in Arizona is already well under way, with Mr. Gallego having announced his bid for Senate in late January.

“I’m better for this job than Kyrsten Sinema because I haven’t forgotten where I came from,” Mr. Gallego told the Associated Press when he announced. “I think she clearly has forgotten where she came from. Instead of meeting with the people that need help, she meets with the people that are already powerful.”

Ms. Sinema, who is looking to protect her seat, hasn’t yet announced her intentions for 2024, but she has been fundraising, albeit not quite as successfully as Mr. Gallego.

In the second quarter of 2023, Ms. Sinema raised $1.7 million compared to Mr. Gallego’s $3.1 million. Ms. Sinema, though, would enter the race with a considerable $10.8 million war chest amassed over her time in the Senate.

“Arizonans are sick of extreme career candidates constantly saying and doing whatever it takes to raise more and more money,” a spokesman for Ms. Sinema said in a statement. “Kyrsten promised Arizonans she’d be an independent Senator who delivers lasting solutions, and that’s exactly what she’s done.”

One ominous sign for Ms. Sinema is her lack of fundraising from small donors, typically defined as those who donate less than $200, which is used as a measure of grassroots support. In the second quarter, she raised less than $9,000 from small donors.

This means most of Ms. Sinema’s cash is coming from political action committees, businesses, and big donors. Mr. Gallego, for comparison, didn’t raise any money from political action committees.

Complicating Ms. Sinema’s decision whether to run is that she consistently polls behind both Mr. Gallego and a slate of potential Republican candidates.

In the most recent poll, from Public Policy Polling, which was done for Mr. Gallego’s campaign in April, Ms. Sinema polled in last place in matchups against businessman Jim Lamon, Sheriff Mark Lamb, and news host Kari Lake.

Ms. Sinema’s best performance was in the matchup involving Messrs. Gallego and Lamon and herself, with the candidates polling at 43 percent, 27 percent, and 16 percent, respectively.

The polling also indicates that Ms. Sinema’s candidacy might pull about as much from the GOP vote pool as from the Democrats in the general election. Currently, the Cook Political Report rates the race as a “toss up.”