(CNN) The string of revelations from Donald Trump Jr.'s meeting with a well-connected Russian lawyer gave more fuel to already intense congressional investigations into potential collusion between the campaign of President Donald Trump and Russia.

The focus quickly turned to Trump Jr., former campaign chairman Paul Manafort and Trump adviser and son-in-law Jared Kushner -- the three people representing Trump in the meeting.

Senate judiciary committee Chairman Chuck Grassley, an Iowa Republican, quickly invited Manafort and Trump Jr. to testify before his committee. Meanwhile, Sen. Mark Warner, the top Democrat of the Senate intelligence committee -- which is directing the lead Russia investigation in the Senate -- said his committee would seek additional documents from Manafort and Kushner.

Here's the state of play for congressional Russia investigations.

1. When will Manafort, Trump Jr. and Kushner testify?

It's unlikely that any of the three major players from the Russia meeting -- Manafort, Kushner or Trump Jr. -- will testify this week, despite at least one urgent request. No such hearings have been scheduled as of Monday afternoon.

The Senate judiciary committee is considering delaying a hearing this week where Grassley had initially hoped that Manafort would testify, a committee spokesperson told CNN. Now, the committee may delay its Wednesday hearing on the Foreign Agents Registration Act until July 26.

Grassley and the top Democrat on the panel, Sen. Dianne Feinstein, had reached out to special counsel Robert Mueller to see if there were any conflicts with hearing from Manafort, as well as Trump Jr., whom the two leaders want to hear from as well.

They so far have not heard back from Mueller's office, the staffer told CNN.

"Sens. Grassley and Feinstein are still working at the staff level to formalize the invitations for additional witnesses," committee spokesman Taylor Foy said. "The committee is considering moving the hearing on enforcement of the Foreign Agents Registration Act.

Donald Trump, Jr. (R) greets his father Republican presidential nominee Donald Trump during the town hall debate at Washington University on October 9 in St Louis, Missouri.

2. Who will get them first?

Count on the Senate intelligence committee to be the most likely venue for all three to testify first, as those committees have functioned as the primary congressional investigations into Russian interference in the election last year.

Senate intelligence committee Chairman Richard Burr and Sen. Mark Warner, the top Democrat on the panel, have aggressively and successfully courted high-profile witnesses that other committees have not had. Shortly after Trump fired then-FBI Director James Comey and details of their private conversations leaked , a mad dash ensued on the Hill to find Comey. Only the Senate intelligence committee succeeded in calling him in -- some Hill investigators said they couldn't get a hold of Comey.

"Officially noticed a hearing for next Wed at 9:30am ET with former FBI Dir Comey. But I still need to speak with him...evidently has a new #" then-Rep. Jason Chaffetz, who was chairing the House oversight committee at the time, tweeted on May 17

Paul Manafort (R), campaign manager for Republican then-presidential candidate Donald Trump, is interviewed by journalist John Dickerson (L) on the floor of the Republican National Convention at the Quicken Loans Arena on July 17, 2016 in Cleveland, Ohio. (Photo by Win McNamee/Getty Images)

3. Who says they testify at all?

Mueller could potentially block their testimony on the Hill in some cases. Grassley said last week that he would defer to Mueller in scheduling Manafort's testimony.

Meanwhile, a partisan tug-of-war is building on the House intelligence committee over how deferential they should be to Mueller, according to Democratic committee sources. While the House probe has not given complete veto power to Mueller to block key witnesses -- like Manafort, Kushner and Trump Jr. -- at least one Republican leader of the probe, Rep. Trey Gowdy, has said he wants to stay far away from the witnesses Mueller's interviewing. Democrats on the probe, meanwhile, say they understand worries about interfering with the federal criminal probe, but they don't want to cede the House's independence.

No final decisions have been made in the House.

The only probe which has flatly denied Mueller's request for a final say in witness testimony is the Senate intelligence committee, according to Democratic committee sources.

Former FBI Director Robert Mueller, special counsel on the Russian investigation, leaves the US Capitol building following a meeting with members of the Senate judiciary committee on June 21.

4. What do investigators want to know?

Broadly, every investigation wants to know about Trump campaign aide communications with Russians. Immediately, the Senate judiciary committee's leaders want to know about the June 2016 meeting with Russian lawyer Natalia Veselnitskaya.

But the Senate intelligence committee, in particular, has maintained a methodical approach to negotiating with witnesses' legal teams, then obtaining and reviewing their documents. News of the June 2016 meeting buoyed the Senate intelligence committee's interest in Trump Jr. in particular -- but Warner has said publicly that they were also asking for additional documents from Manafort and Kushner.

Warner, and others on the committees, have regularly noted they only get one bite at the apple with some of these high-profile witnesses and they don't want to blow their chance without having first reviewed all the evidence they can.

All of which points to it taking a while before any big names like Manafort, Kushner and Trump Jr. appear on the Hill.