(CNN)Maryland Republican Gov. Larry Hogan made it official on Tuesday: He will not run against Democratic Sen. Chris Van Hollen this year.

       "I don't aspire to be a senator, and that fact has not changed," Hogan told reporters.

       And with that, Senate Republicans' best chance of expanding the current 2022 map just disappeared.

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       Without the popular Hogan running, Maryland Republicans have little chance of even keeping it close against Van Hollen, who won with 61% of the vote in 2016.

       At the moment, there are six Senate races that both sides agree are toss ups. Democrats are seeking reelection in three of those races: Arizona (Mark Kelly), Georgia (Raphael Warnock) and Nevada (Catherine Cortez Masto). Another features a Republican running for another term: Wisconsin (Ron Johnson). And two are open seats due to Republican retirements: North Carolina and Pennsylvania.

       Barring some sort of unforeseen cataclysm, those races will be close from now until Election Day. It's the races at the next level of competitiveness -- where one side is favored, but the other side has a shot -- that could wind up determining who holds the majority come January 2023.

       (Sidebar: Democrats currently hold 50 seats and the majority because of Vice President Kamala Harris' tie-breaking vote.)

       In that next tier of Democratic-held seats is where Republicans are struggling on candidate recruitment. While New Hampshire Sen. Maggie Hassan is still considered vulnerable, Republicans have a harder climb than they would have if Gov. Chris Sununu had run. Ditto Colorado, where the GOP seems to be nowhere in terms of recruiting a top-tier candidate to take on Sen. Michael Bennet. Now, add Maryland to that list.

       Democrats, by contrast, have a few longer-shot opportunities among GOP-controlled seats. They got their preferred candidates in Florida (Rep. Val Demings) and Ohio (Rep. Tim Ryan) to run, and effectively cleared the primary field for each of them. Missouri's open seat is another longer-shot chance if Republicans nominate controversial former Gov. Eric Greitens.

       It's possible, of course, that the national environment is quite favorable to Republicans in November, allowing them to hold all of their endangered seats while picking up at least one of Democrats' most at-risk seats. If Republicans do that, they have the majority.

       But Republicans would desperately like to give themselves a few more scenarios to get to the majority -- and that requires an expansion of the current playing field of competitive races.

       The Point : Convincing Hogan to run for Senate was always a very long shot. But with him out, Maryland is officially off the board of races Republicans have hopes to make competitive.